Fix channel autocomplete and fix channel member query to ignore deleted channels (#4371)

store/sql_channel_store.go

@@ -1040,6 +1040,7 @@ func (s SqlChannelStore) GetMembersForUser(teamId string, userId string) StoreCh
             INNER JOIN Channels c
                 ON c.Id = cm.ChannelId
                 AND (c.TeamId = :TeamId OR c.TeamId = '')
+                AND c.DeleteAt = 0
             WHERE cm.UserId = :UserId
 		`, map[string]interface{}{"TeamId": teamId, "UserId": userId})