Fix decoration behavior when passing over with button pressed

Fix the decoration resizing or moving the window when passing over it
with the mouse button pressed, but which was not clicked over the decoration.

Change-Id: If5d1d041ae6f80a07ce83bdca92dab35f721f2eb
Reviewed-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
Reviewed-by: Andy Nichols <andy.nichols@digia.com>