desktop-shell: Reject resize if we're already grabbed
desktop-shell: Reject resize if we're already grabbed

This rejects resizing a window that's currently being moved.  This can
be done using a touch screen and a pointer or just two seats.

sir-murray/weston,Fantu/compositor-spice,giucam/weston,xorgy/weston,udoprog/weston,Fantu/compositor-spice,udoprog/weston,kwm81/weston,xorgy/weston,kwm81/weston,krezovic/weston,Tarnyko/weston-xdg_surface_present,jonnylamb/weston,giucam/weston,Fantu/compositor-spice,Gnurou/weston,jonnylamb/weston,krezovic/weston,Gnurou/weston,Tarnyko/weston-xdg_surface_present,mchalupa/weston,mchalupa/weston,eyolfson/weston,eyolfson/weston,sir-murray/weston