Scans a single file and adds all fonts found to set.
If force is FcTrue, then the file is scanned even if
associated information is found in cache. If
file is a directory, it is added to
dirs. Whether fonts are found depends on fontconfig
policy as well as the current configuration. Internally, fontconfig will
ignore BDF and PCF fonts which are not in Unicode (or the effectively
equivalent ISO Latin-1) encoding as those are not usable by Unicode-based
applications. The configuration can ignore fonts based on filename or
contents of the font file itself. Returns FcFalse if any of the fonts cannot be
added (due to allocation failure). Otherwise returns FcTrue.