Prevent LLFace::getGeometryVolume from overwriting vbos past their end.

Possible fix for a crash in LLFace::getGeometryVolume()
Patch by NickyD/Firestorm
Crash signature: 14 and 20
Remove attachments from the avatar's attached list before destroying them.
This should prevent the idle callbacks from accessing deleted attachments when looking for the CCS signature.
Merge branch 'master' of https://github.com/MelanieT/SingularityViewer
Merge branch 'master' of git://github.com/Lirusaito/SingularityViewer