Prevent store.push when store is destroying
Prevent store.push when store is destroying

Fixes the `_containerCache is undefined` error

FirebaseExtended/emberfire,leifcr/emberfire,IsaiahJTurner/emberfire,leifcr/emberfire,IsaiahJTurner/emberfire,rtablada/emberfire,MattMSumner/emberfire,FirebaseExtended/emberfire,MattMSumner/emberfire,FirebaseExtended/emberfire,rtablada/emberfire,FirebaseExtended/emberfire