x11: Don't ignore button releases after a wmspec move/resize
_gdk_x11_moveresize_configure_done() isn't called for wmspec
moves/resizes so we don't have a way to notice when a wmspec
move/resize ends and consequently untrigger the sending of
_NET_WM_MOVERESIZE_CANCEL which results in this message always being
sent on the next button release event. In that case we are marking
that event as handled so it isn't processed further which breaks
button press/release event handling in several widgets.
To fix this we simply allow the normal event handling machinery to run
after sending the _NET_WM_MOVERESIZE_CANCEL message.