Primary font ignores the fontconfig's charset property. #30

I reported an issue several days ago. Maybe at that time I didn't make myself clear. I guess that the following source blocks cause this issue.

In src/ft/mod.rs :
In my case, the function load_face_with_glyph(...) has never been called. Because in face_for_glyph(...), it always returns early inside the 'if let' block.

In the get_face(...) function, the 'coverage' of the 'Fallbacklist' struct doesn't include the charset of the primary font. So setting the charset property of the first matched font (the primary font) in fonts.conf doesn't work if no fallback is happened.