window: Don't crash if a cursor image failed to load.
window: Don't crash if a cursor image failed to load.

Signed-off-by: Dima Ryazanov <bed3f98d0a894717be46c58ffa90302af9946688@gmail.com>

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