Bogus unreachability message when multiple font formats provided

```
What steps will reproduce the problem?
1. Create an EPUB book containing an @font-face rule with multiple formats,
e.g.

@font-face {
font-family: 'GFS Didot';
font-style: normal;
font-weight: normal;

src: url('fonts/GFSDidot/GFSDidot.ttf') format('truetype'), url('fonts/GFSDidot/GFSDidot.otf') format('opentype'), local('GFS Didot Regular'), local('GFSDidot-Regular');
}

2. Include both the TTF and OTF versions of the file.

What is the expected output? What do you see instead?

I would not expect any warning. Both files can potentially be used, depending
on what font formats the particular reader supports. Instead, the validator
warns that the OTF file is unreachable.

What version of the product are you using? On what operating system?

0.7.2/Mac OS X

```

Original issue reported on code.google.com by `dgatwoo...@gmail.com` on 24 Nov 2011 at 8:07

Attachments:
- [calibreFontBug.epub](https://storage.googleapis.com/google-code-attachments/flightcrew/issue-28/comment-0/calibreFontBug.epub)