fix [#34098] Crash after using Decimate or Remesh modifiers

converting a derived mesh to a mesh didnt clear its selection history, which could be invalid after applying a modifier.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54292 954f8c5b-7b00-dc11-b283-0030488c597c