fontselect: leave returned struct in a valid state on error
fontselect: leave returned struct in a valid state on error

This fixes a double-free in be0d1613f79a95073d18d96a60e1394abf9316a2

MrSmile/libass,Akemi/libass,libass/libass,MrSmile/libass,ShiftMediaProject/libass,Akemi/libass,xbmc/libass,Akemi/libass,xbmc/libass,astiob/libass,libass/libass,astiob/libass,ShiftMediaProject/libass