compositor: initialise segv_action.sa_mask
compositor: initialise segv_action.sa_mask

Valgrind complained sa_mask member is not initialised, fix that.

Signed-off-by: Pekka Paalanen <6c0263d81461c956d504307112a4ce25eaacc3d1@gmail.com>

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