shaper: actually correctly handle @font advance
shaper: actually correctly handle @font advance

The code was confusing glyph index and Unicode codepoint.
256df617 attempted a fix but merely moved the wrong code.

Fixes Google Code issue #94.

Vertical ligatures are possibly still broken, but
horizontal ligatures and non-ligatures are correct now.

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