[Fontconfig] fc-cache sometimes looses fonts

[Patrick Lam]

Mike FABIAN wrote:
> And now the font appears to be gone:
> 
>     mfabian at magellan:~/.fonts$ fc-list : family file | grep -i zenkai
>     mfabian at magellan:~/.fonts$

Not only that, but .fonts.cache-2 then becomes corrupted.  Interesting,
eh?  This seems to be the source of the cache corruption; if you run
fc-cat on fonts.cache-2 at this point, you'll find that it segfaults.

I added an extra FcDirScan to this codepath.  I believe that this fixes
the cache corruption problems.  I hate to admit that I'm not entirely
sure why the old code had cache corruption problems, but I'll look into
that just a bit longer.  It seems to make sense though.

pat