#42 crashes with buggy fonts

[IOhannes m zmölnig]

a user of mine reported a crasher bug when rendering a specific font.

we tried hunting down the font, and it seems that
- the font is buggy (e.g. containing self-intersecting glyphs)
- FTGL crashes

the buggy font is Beans

doing a quick check with FTGLDemo (2.1.3~rc5) shows that FTGL is indeed crashing:
- start ./FTGLDemo /path/to/Beams.ttf
- (rendering seems to work though there are a lot of artefacts)
- type Left
- CRASH

alternatively running ./FTGLMFontDemo /path/to/Beams.ttf immediately crashes.

the problem persists with the current SVN version of FTGL.

the original bug-report (containing an assertion error and the output of the fontforge validation of the Font=, can be found here