Fix Hinting again

Commit 05eb520 missed some duplicated bits in ass_shaper.c.

<wm4> oh crap
<zgreg> oh crap indeed

Instead of duplicating the logic in ass_shaper.c, just change the
glyphs before they even get into processing. This way, all code
reading the font size etc. is affected. This essentially reverts
commit c207000c, because it's not needed anymore.
Cosmetics: remove repetition
ass_shaper: changing scale_x/y starts a new glyph run

Since font_size is usually normalized to 256, scale_x/y has to be used
for this purpose.