Don't do frame processing if ast_read() returned NULL.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@89886 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/autoservice.c

@@ -89,6 +89,9 @@ static void *autoservice_run(void *ign)
 		chan = ast_waitfor_n(mons, x, &ms);
 		if (chan) {
 			struct ast_frame *f = ast_read(chan);
+	
+			if (!f)
+				continue;
 			
 			/* Do not add a default entry in this switch statement.  Each new
 			 * frame type should be addressed directly as to whether it should