[smooth] Switch to vertical bisections.

With horizontal bisections, the smallest section is a whole single
scanline. Almost horizontal lines or other complex scanlines can
easily overflow the rendering pool. Switching to vertical bisections
splits the scanlines and should rule out the overflows.  Fixes #1269.

* src/smooth/ftgrays.c (gray_convert_glyph): Bisect vertically.
1 file changed