input: Reset keyboard state when releasing last seat keyboard
input: Reset keyboard state when releasing last seat keyboard

Don't rely on the input driver to properly send button-up events for
every pressed key.

Signed-off-by: Jonas Ådahl <67dcd8a17e758192e0cbb577ce1d62cc7da6cf49@gmail.com>

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