Fixes for Coverity-reported issues: fontforge/parsepdf.c

A mix of commits that solve many of the various issues reported by Coverity for file parsepdf.c.  Some of these are separated out into individual commits to allow description of the individual problems.  A number of minor fixes are smashed into the last commit.  How well each could be tested is noted in each commit/area.

While trudging through the Coverity reports does not seem very worthwhile, the second commit "Coverity parsepdf.c toknames[] PDF parsing bug!" is the best counter-answer.  Horrible bug unnoticed for 6 years because it was *so easy to overlook*!

A couple Coverity reports remain for this file, that defied easy fixing or looked like too much to fix without rewriting sections.