bridge_native_rtp: Fix crash involving masquerade

It is possible for a channel to be masqueraded out of a bridge which
means it may no longer have RTP glue to check upon leaving said bridge.
If this situation occurred (it's possible at least during dial and call
pickup) then Asterisk would crash. This change makes sure the glue is
checked before use.

(closes issue AST-1290)
Reported by: John Bigelow
........

Merged revisions 409900 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@409904 65c4cc65-6c06-0410-ace0-fbb531ad65f3

bridges/bridge_native_rtp.c

@@ -452,9 +452,19 @@ static void native_rtp_bridge_leave(struct ast_bridge *bridge, struct ast_bridge
 	native_rtp_bridge_framehook_detach(bridge_channel);
 
 	glue = ast_rtp_instance_get_glue(ast_channel_tech(bridge_channel->chan)->type);
+	if (!glue) {
+		return;
+	}
+
 	glue->get_rtp_info(bridge_channel->chan, &instance);
-	glue->get_vrtp_info ? glue->get_vrtp_info(bridge_channel->chan, &vinstance) : AST_RTP_GLUE_RESULT_FORBID;
-	glue->get_trtp_info ? glue->get_trtp_info(bridge_channel->chan, &tinstance) : AST_RTP_GLUE_RESULT_FORBID;
+
+	if (glue->get_vrtp_info) {
+		glue->get_vrtp_info(bridge_channel->chan, &vinstance);
+	}
+
+	if (glue->get_trtp_info) {
+		glue->get_trtp_info(bridge_channel->chan, &tinstance);
+	}
 
 	/* Tear down P2P bridges */
 	if (instance) {