Fix typo in chan_sip

The conditional expressions of the 'if' operators
situated alongside each other are identical.

Change-Id: I652b6dcddb3be007e669a6aa8107edb31a1ddafb

channels/chan_sip.c

@@ -2512,7 +2512,7 @@ static void sip_threadinfo_destructor(void *obj)
 	struct sip_threadinfo *th = obj;
 	struct tcptls_packet *packet;
 
-	if (th->alert_pipe[1] > -1) {
+	if (th->alert_pipe[0] > -1) {
 		close(th->alert_pipe[0]);
 	}
 	if (th->alert_pipe[1] > -1) {