Workaround for TrueType fonts with exotic cmap tables (bug 1057544)

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1057544.

The TrueType font used in the file has a (0, 1) cmap table, which we currently don't support. Adding support for more kinds of cmap tables is tracked in #5231, which I'll happily leave for @brendandahl when he gets back :-)

In the meantime, I'm submitting this patch to workaround the bug. Prior to #4259, we used to default to a (3, 1) cmap table when no standard one was found, which is why I hope this patch will be OK as a temporary fix.

*Note:* I'm expecting some movement, for the better, on issue4800.pdf since it has a (0, 1) cmap.