window: Don't overwrite window->allocation until we've done the resize
window: Don't overwrite window->allocation until we've done the resize

This way we can actually detect whether or not a window resizes.

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