client: Don't forget to init and destroy mutex
client: Don't forget to init and destroy mutex

These chunks were dropped at some point, thanks to David Herrmann for
spotting the omission.

eyolfson/wayland,eyolfson/wayland,eyolfson/wayland,tulcod/wayland,sir-murray/wayland,abooij/wayland,bitfactor/wayland,tulcod/wayland,sir-murray/wayland,abooij/wayland,abooij/wayland,bitfactor/wayland,mchalupa/wayland,tulcod/wayland,mchalupa/wayland,sir-murray/wayland,bitfactor/wayland,mchalupa/wayland