Fixed exception raised in admin when changing slug of publishable object without main placement.
Fixed exception raised in admin when changing slug of publishable object without main placement.

git-svn-id: f4376cbc2d5ef7c314d50186b99f5769c0e6542f@1805 2d143e24-0a30-0410-89d7-a2e95868dc81

petrlosa/ella,whalerock/ella,WhiskeyMedia/ella,ella/ella,petrlosa/ella,MichalMaM/ella,MichalMaM/ella,whalerock/ella,whalerock/ella,WhiskeyMedia/ella