[REG 4.8.6->5.4.1] Windows: Widget with Qt::Popup window flag can’t be closed if there is no other visible widget

When a widget is created with Qt::Popup window flag it is not closed when clicking outside the widget. The attached example shows how a popup widget can be opened by clicking the system tray icon, but it is not closed when you click outside the widget.

With 4.8.6 the popup widget was closed when clicking outside the widget as expected.

Steps to reproduce:

• Launch attached example qtbug44928 which opens a popup via timer
• Note: Popup widget is opened
• Click outside the popup widget
• EXPECTED: Widget is closed
• ACTUAL: Widget stays open

• Repeat, but click inside first, then outside. Pop up closes

• Repeat with -s, showing the main widget: Pop up can be closed by clicking outside