ADS Overlays remain visible if Escape Key is pressed

If a Floating Widget is dragged around and the dragging is canceled, then it may happen, that the overlays are not hidden.

If the dragging of the window is canceled via escape key, then the window is moved to its initial drag position. If the mouse cursor is outside of the Window after this move, then a QEvent::NonClientAreaMouseButtonRelease event will be generated, which in turn docks the Window into the selected drop position.
If the mouse cursor is inside of the Window after the Window has been reset to its initial position, a QEvent::MouseButtonRelease will be generated, that is not handled yet which in turn will not hide the overlays.

The attached gif shows this problem. The Window is moved downward. Then the escape key is pressed and the Window is rest to its initial position. Because the mouse is in the client are of the Window now, a QEvent::MouseButtonRelease event is generated.

Originally reported here:
https://github.com/githubuser0xFFFF/Qt-Advanced-Docking-System/issues/143