Fix a warning due to added constness
Fix a warning due to added constness

pigoz/libass-ct,richardpl/libass,stps/libass,grigorig/libass,ShiftMediaProject/libass,sanyaade-g2g-repos/libass,grigorig/libass,stps/libass,vault/libass,rhlee/libass,pigoz/libass-ct,tgoyne/libass,ShiftMediaProject/libass,tgoyne/libass,sanyaade-g2g-repos/libass,asimonov-im/libass,torque/libass,blinkseb/libass,MrSmile/libass,mwgoldsmith/libass,torque/libass,libass/libass,vault/libass,blinkseb/libass,pigoz/libass-ct,richardpl/libass,xbmc/libass,blinkseb/libass,xbmc/libass,mwgoldsmith/libass,Akemi/libass,MrSmile/libass,sanyaade-g2g-repos/libass,Distrotech/libass,rhlee/libass,mwgoldsmith/libass,asimonov-im/libass,torque/libass,richardpl/libass,Distrotech/libass,tgoyne/libass,Akemi/libass,astiob/libass,Akemi/libass,rhlee/libass,astiob/libass,libass/libass,Distrotech/libass,stps/libass