gtkwindow: claim the press sequence when clicking on the titlebar
gtkwindow: claim the press sequence when clicking on the titlebar

This event might not have an action yet, but certainly accounts, and
should be triggering recognition.

This fixes a crash when attempting to drag CSD windows through touch. As
since cfaec2d2f542, gtk_gesture_single_get_current_sequence() would
rightfully return NULL if the gesture didn't enter recognition, making
event lookup fail.

grubersjoe/adwaita,jadahl/gtk,Lyude/gtk-,davidgumberg/gtk,Adamovskiy/gtk,Adamovskiy/gtk,davidgumberg/gtk,davidgumberg/gtk,ahodesuka/gtk,Adamovskiy/gtk,Lyude/gtk-,ahodesuka/gtk,alexlarsson/gtk,ahodesuka/gtk,Adamovskiy/gtk,jigpu/gtk,davidgumberg/gtk,jigpu/gtk,Lyude/gtk-,jigpu/gtk,davidgumberg/gtk,ahodesuka/gtk,Adamovskiy/gtk,davidgumberg/gtk,grubersjoe/adwaita,jadahl/gtk,davidgumberg/gtk,jadahl/gtk,grubersjoe/adwaita,jigpu/gtk,chergert/gtk,ahodesuka/gtk,chergert/gtk,chergert/gtk,jadahl/gtk,ahodesuka/gtk,jigpu/gtk,grubersjoe/adwaita,chergert/gtk,davidgumberg/gtk,Lyude/gtk-,jigpu/gtk,Lyude/gtk-,chergert/gtk,Lyude/gtk-,alexlarsson/gtk,alexlarsson/gtk,chergert/gtk,jigpu/gtk,grubersjoe/adwaita,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,ahodesuka/gtk,chergert/gtk,grubersjoe/adwaita,jadahl/gtk,chergert/gtk,alexlarsson/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jadahl/gtk,grubersjoe/adwaita,jigpu/gtk,Adamovskiy/gtk,Lyude/gtk-,ahodesuka/gtk,jadahl/gtk,Lyude/gtk-,grubersjoe/adwaita,jadahl/gtk,alexlarsson/gtk