avoiding warning, fixing potential bug (backported from 1.2)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.2@45090 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_misdn.c

@@ -2864,6 +2864,8 @@ static struct chan_list *find_holded_l3(struct chan_list *list, unsigned long l3
 			) 
 			return help;
 	}
+
+	return NULL;
 }
 
 static void cl_queue_chan(struct chan_list **list, struct chan_list *chan)