Hang during drag and drop [REG]

Application may hang under certain preconditions during drag and drop.

It looks like it is caused by this commit https://github.com/qt/qtbase/commit/9ff5b886fade489b7cc268626f518145650f6b2c

Now it takes a window that is considered under mouse by QWindowsContext.

The problem if it picks WS_EX_LAYERED window, which is transparent and does not receive any messages, and the application hangs on GetMessage forever.

This is how QWindowsContext picks a window in short

1. getWindowUnderPointer() returns target window OR first window under mouse (on desktop) if it has a capture
2. picked window is then saved to QWindowsContext as under point if it does not have a capture

So, the problem occurs whenever capture changed between 1 and 2. This happens on mouse release. getWindowUnderPointer() picks layered window (transparent) while capture belongs to the source window. Then capture released in QWindowsPointerHandler::handleCaptureRelease (because of event type QEvent::MouseButtonRelease) and layered window saved in QWindowsPointerHandler::handleEnterLeave (since capture released).

Sample app attached. Launch and try to drag "Drag me" quickly, e.g., press LMB->short mouse move->release LMB. Try a few times if needed