coretext: use SAFE_CFRelease() for robustness
coretext: use SAFE_CFRelease() for robustness

CFRelease(NULL) can crash. While we're still not sure which CoreText API
calls can fail etc. (thanks Apple), this should fix a couple of
theoretically possible crashes.

MrSmile/libass,MrSmile/libass,torque/libass,sanyaade-g2g-repos/libass,xbmc/libass,Akemi/libass,astiob/libass,ShiftMediaProject/libass,Akemi/libass,sanyaade-g2g-repos/libass,Akemi/libass,stps/libass,libass/libass,stps/libass,stps/libass,xbmc/libass,mwgoldsmith/libass,grigorig/libass,libass/libass,grigorig/libass,torque/libass,sanyaade-g2g-repos/libass,astiob/libass,torque/libass,mwgoldsmith/libass,ShiftMediaProject/libass,mwgoldsmith/libass