Fix #35570, old group nodes with empty socket name strings crash. The identifier assignment was not taking potentially empty name strings into account. In addition some of the BLI_uniquename calls were
not passing a valid defname parameter, also crashing.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57139 954f8c5b-7b00-dc11-b283-0030488c597c