Fix for [#34913] Freestyle: Problem w/ Edge Marks combined w/ Collision.

Freestyle edge marks were messed up with Collision and other physics mesh modifiers.
The issue was due to copied Vlak instances without resetting edge marks to proper values.

Also made minor changes for avoiding unnecessary hash table lookups, and added an
assertion to check potential buffer overrun.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56031 954f8c5b-7b00-dc11-b283-0030488c597c