Fix potential memory leak

Fix potential memory leak

xkb_state_new uses calloc and may fail in a rare case, which would cause a memory leak.
Note that xkb_state_unref checks if the parameter given is not null (!state) before freeing.
Calls to xkb_state_new have been grouped to remove code duplication.

Signed-off-by: Elouan Martinet <exa@elou.world>