Fix off-by-one error in \fad, \fade
Fix off-by-one error in \fad, \fade

Typical greater vs. greater-or-equal case. This especially fixes fades
with zero delays. A zero delay in the two-argument form means no fade at
all, but previously this faded over a single frame, since the code used
"greater" semantics, while "greater or equal" is required here.

Notably, this avoids blinking/flickering in some tightly timed karaoke
scripts.

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