Bold/italic: interpret -1 as "true"
Bold/italic: interpret -1 as "true"

Interpret the value -1 as "true", as specified in the ASS
specifications.  Otherwise, clamp the value to 0 for other values <
0, so these are interpreted as "false".

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