chan_pjsip.c: Fix uninitialized cause value on failure.

Change-Id: I3f9dd3c31bd582e54a30381500077de2319d8cc3

channels/chan_pjsip.c

@@ -2442,6 +2442,8 @@ static struct ast_channel *chan_pjsip_request_with_stream_topology(const char *t
 
 	req_data.topology = topology;
 	req_data.dest = data;
+	/* Default failure value in case ast_sip_push_task_synchronous() itself fails. */
+	req_data.cause = AST_CAUSE_FAILURE;
 
 	if (ast_sip_push_task_synchronous(NULL, request, &req_data)) {
 		*cause = req_data.cause;