Entering text causes the application to crash on Symbian

When entering text with fullscreen FEP to lineedit when lineedit isn't fully visible and causing QWidget scroll event to make the character visible we get Kern-Exec 3 as the backingstore is null.
The bug here is that widget backing store is deleted when FEP is the fullscreen foreground window.

Offending lines can be found from gui/kernel/qapplication_s60.cpp:

    case EEventWindowVisibilityChanged:
...
            if (visChangedEvent->iFlags & TWsVisibilityChangedEvent::ENotVisible) {
                delete w->d_func()->topData()->backingStore;
                w->d_func()->topData()->backingStore = 0;
 ... 

Deletion must not be done if we are running fullscreen FEP.

Callstack is from QWebview based app showing google front page and being scrolled enough to right to not to show the first character.

61 QWidgetBackingStore::bltRect() C:\repos\qt-webkit\src\gui\painting\qbackingstore.cpp:264 0x04dc9c88
60 QWidgetPrivate::scrollRect() C:\repos\qt-webkit\src\gui\painting\qbackingstore.cpp:1004 0x04dcc5ee
59 QWidgetPrivate::scroll_sys() C:\repos\qt-webkit\src\gui\kernel\qwidget_s60.cpp:841 0x04cf0f06
58 QWidget::scroll() C:\repos\qt-webkit\src\gui\kernel\qwidget.cpp:9955 0x04ccc317
57 QWebPageWidgetClient::scroll() C:\repos\qt-webkit\src\3rdparty\webkit\WebKit\qt\Api\qwebpage.cpp:178 0x07f30173
56 WebCore::ChromeClientQt::scroll() C:\repos\qt-webkit\src\3rdparty\webkit\WebKit\qt\WebCoreSupport\ChromeClientQt.cpp:329 0x07f4f22b
55 WebCore::Chrome::scroll() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\page\Chrome.cpp:78 0x07c4246d
54 WebCore::ScrollView::scrollContents() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\platform\ScrollView.cpp:513 0x07cb6d37
53 WebCore::ScrollView::valueChanged() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\platform\ScrollView.cpp:263 0x07cb5d4e
52 WebCore::FrameView::valueChanged() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\page\FrameView.cpp:1447 0x07c6fc52
51 WebCore::Scrollbar::setCurrentPos() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\platform\Scrollbar.cpp:277 0x07cb2c4b
50 WebCore::Scrollbar::setValue() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\platform\Scrollbar.cpp:97 0x07cb215d
49 WebCore::ScrollView::updateScrollbars() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\platform\ScrollView.cpp:439 0x07cb6794
48 WebCore::ScrollView::setScrollPosition() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\platform\ScrollView.cpp:308 0x07cb5f83
47 WebCore::ScrollView::scrollRectIntoViewRecursively() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\platform\ScrollView.cpp:275 0x07cb5de2
46 WebCore::FrameView::scrollRectIntoViewRecursively() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\page\FrameView.cpp:872 0x07c6d577
45 WebCore::RenderLayer::scrollRectToVisible() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\rendering\RenderLayer.cpp:1265 0x07da898c
44 WebCore::RenderLayer::scrollRectToVisible() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\rendering\RenderLayer.cpp:1268 0x07da89af
43 WebCore::RenderLayer::scrollRectToVisible() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\rendering\RenderLayer.cpp:1268 0x07da89af
42 WebCore::Frame::revealSelection() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\page\Frame.cpp:1326 0x07c64e63
41 WebCore::Editor::revealSelectionAfterEditingOperation() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\editing\Editor.cpp:2559 0x0784c2bd
40 WebCore::Editor::setIgnoreCompositionSelectionChange() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\editing\Editor.cpp:2569 0x0784c2f7
39 WebCore::Editor::setComposition() C:\repos\qt-webkit\src\3rdparty\webkit\WebCore\editing\Editor.cpp:1420 0x07849b98
38 QWebPagePrivate::inputMethodEvent() C:\repos\qt-webkit\src\3rdparty\webkit\WebKit\qt\Api\qwebpage.cpp:1261 0x07f3372f
37 QWebPage::event() C:\repos\qt-webkit\src\3rdparty\webkit\WebKit\qt\Api\qwebpage.cpp:2567 0x07f38bc7
36 QWebView::inputMethodEvent() C:\repos\qt-webkit\src\3rdparty\webkit\WebKit\qt\Api\qwebview.cpp:947 0x07f3c7b3
35 QWidget::event() C:\repos\qt-webkit\src\gui\kernel\qwidget.cpp:8064 0x04cc958e
34 QWebView::event() C:\repos\qt-webkit\src\3rdparty\webkit\WebKit\qt\Api\qwebview.cpp:657 0x07f3bf8d
33 QApplicationPrivate::notify_helper() C:\repos\qt-webkit\src\gui\kernel\qapplication.cpp:4242 0x04c7b36c
32 QApplication::notify() C:\repos\qt-webkit\src\gui\kernel\qapplication.cpp:4207 0x04c7a9fa
31 QCoreApplication::notifyInternal() C:\repos\qt-webkit\src\corelib\kernel\qcoreapplication.cpp:704 0x044dbd2b
30 QCoreApplication::sendEvent() C:\repos\qt-webkit\src\corelib\kernel\qcoreapplication.h:215 0x044589c3
29 QInputContext::sendEvent() C:\repos\qt-webkit\src\gui\inputmethod\qinputcontext.cpp:280 0x04ba4fe0
28 QCoeFepInputContext::StartFepInlineEditL() C:\repos\qt-webkit\src\gui\inputmethod\qcoefepinputcontext_s60.cpp:499 0x04ba72b6
27 0x7051A954( avkonfep.dll )() 0x7051a954
26 0x70512D3C( avkonfep.dll )() 0x70512d3c
25 0x7054328F( avkonfep.dll )() 0x7054328f
24 0x7052E062( avkonfep.dll )() 0x7052e062
23 0x7053B1DF( avkonfep.dll )() 0x7053b1df
22 0x705049DF( avkonfep.dll )() 0x705049df
21 0x70527079( avkonfep.dll )() 0x70527079
20 0x406010BA( cone.dll )() 0x406010ba
19 0x4060187D( cone.dll )() 0x4060187d
18 0x40B4AB13( eikcore.dll )() 0x40b4ab13
17 0x56A8245( avkon.dll )() 0x056a8245
16 QS60MainAppUi::HandleWsEventL() C:\repos\qt-webkit\src\gui\s60framework\qs60mainappui.cpp:184 0x04dd09a3
15 0x4060A68D( cone.dll )() 0x4060a68d
14 0x60002336( euser.dll )() 0x60002336
13 QEventDispatcherSymbian::processEvents() C:\repos\qt-webkit\src\corelib\kernel\qeventdispatcher_symbian.cpp:736 0x0450ffc5
12 QEventDispatcherS60::processEvents() C:\repos\qt-webkit\src\gui\kernel\qeventdispatcher_s60.cpp:74 0x04cecdb5
11 QEventLoop::processEvents() C:\repos\qt-webkit\src\corelib\kernel\qeventloop.cpp:149 0x044d9180
10 QEventLoop::exec() C:\repos\qt-webkit\src\corelib\kernel\qeventloop.cpp:201 0x044d9379
9 QCoreApplication::exec() C:\repos\qt-webkit\src\corelib\kernel\qcoreapplication.cpp:981 0x044dc363
8 QApplication::exec() C:\repos\qt-webkit\src\gui\kernel\qapplication.cpp:3570 0x04c787b9
7 main() C:\webviewclient\main.cpp:53 0x00401188
6 QtMainWrapper() C:\repos\qt-webkit\src\s60main\qts60main_mcrt0.cpp:87 0x00402fc1
5 E32Main() C:\repos\qt-webkit\src\s60main\qts60main.cpp:57 0x00402dfc
4 _E32Startup() L:\src\cedar\generic\base\e32\euser\epoc\win32\uc_exe.cpp:83 0x004024c8
3 0x8E7947F( ekern.exe )() 0x08e7947f
2 0x8E77987( ekern.exe )() 0x08e77987
1 0x7C80B50B( KERNEL32.dll )() 0x7c80b50b