Ignore global advance width unconditionally

Ignore global advance width unconditionally

Some (arguably) broken CJK fonts claim to have a fixed advance width,
but they actually use two different widths for half-width and full-width
characters. Even worse, some use proportional width.
This can cause problems under certain circumstances.  A big project
(Cairo) uses a FreeType load flag to ignore the global advance width
for such fonts, so I assume it can be used safely. Let's do it just
like them.