fix for KVO: removing the last observer would trigger a setObservationInfo:nil, which would access the already-released observationInfo dictionary
fix for KVO: removing the last observer would trigger a setObservationInfo:nil,
which would access the already-released observationInfo dictionary


git-svn-id: 728ffa388f20071a20a4b19b45cfa0b6da7e7a99@169 43251c19-cd1f-0410-9ec0-95c558c233a8

wenq1/cocotron,farcaller/cocotron