[AC21.5] Catch errors in FcNameParse

21.5 I mentioned in response to Marcus's patch for the vdb in darwin/x86_64 that I was still having problems. It turns out that for some reason FcNameParse fails to parse certain fontconfig fontnames. I don't know the root cause (I suspect a bug in fontconfig's parser for charset objects but haven't confirmed -- FcNameParse usually is happy to just ignore any part of the spec it can't handle). The attached patch may be overkill; it's hard to imagine that users will be specifying charsets by hand, and every other bogus spec I tried produced an FcPattern. It's also very inefficient, but I don't notice any difference (parsing filenames is unlikely to happen very often, and the situation where I have actually used fc-name-parse-harder is pretty rare). On balance, I'm inclined to apply as-is. I will wait a few days for contrary opinion.