Handling `not_found` during notify update listener

When the compaction finishes, it checks if it caught up with the updater, or if there are changes that need to be applied to the compacted file as well. It is done with `couch_set_view_util:missing_changes_count/2`, with passing in the seq numbers of the compacted view and the current group. If the group information of the updater didn't receive any update yet, it won't show up as being different from the compacted file. Hence the compactor will stop the updater, switch over to the compacted file and restart the updater. If at this point rebalance stopped, if compacted header don't have this partid(which is monitored during movement of vbs and now undoing), call will return not_found. This not_found is not handled during the filter of vbs and compaction won't finish.