Don't crash on INFO automon request with no channel

AST-2011-014. When automon was enabled in features.conf, it was possible
to crash Asterisk by sending an INFO request if no channel had been
created yet.

(closes issue ASTERISK-18805)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.6.2@347530 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -17417,11 +17417,18 @@ static void handle_request_info(struct sip_pvt *p, struct sip_request *req)
 			per device. I don't want incoming callers to record calls in my
 			pbx.
 		*/
-		/* first, get the feature string, if it exists */
+		
 		struct ast_call_feature *feat;
 		int j;
 		struct ast_frame f = { AST_FRAME_DTMF, };
 
+		if (!p->owner) {        /* not a PBX call */
+			transmit_response(p, "481 Call leg/transaction does not exist", req);
+			sip_scheddestroy(p, DEFAULT_TRANS_TIMEOUT);
+			return;
+		}
+
+		/* first, get the feature string, if it exists */
 		ast_rdlock_call_features();
 		feat = ast_find_call_feature("automon");
 		if (!feat || ast_strlen_zero(feat->exten)) {