Blender Git Loki

Fix T46456: Crash when aborting stroke while using dyntopo.

Basically, the 'fake undo' restoring orig coordinates in this case cannot work with dyntopo,
since it assumes nothing was added/removed.

For now, just prevent this 'restoration' when dyntopo is used, this is no ideal solution
from user PoV - but it's better than plain ugly crash!

Complete solution seems much more involved and outside of scope of bug handling, added a TODO note:
http://wiki.blender.org/index.php/Dev:Source/Development/Todo/Tools#Sculpting