DistributedGroupStore: not updating groupIdTable on startup

When DistributedGroupStore is activated it can receive its group information from another peer in a cluster. If this is the case, the groupStoreEntriesByKey field will be populated but the groupEntriesById won't be synchronized with it.

When it tries to use the groupEntriesById it will cause NullPointerException as it is empty. This happens when it tries to audit the groups and finds a group is missing (groupMissing()).