small bug

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@13408 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/switch_rtp.c

@@ -553,7 +553,9 @@ SWITCH_DECLARE(void) switch_rtp_shutdown(void)
 	switch_mutex_unlock(port_lock);
 
 #ifdef ENABLE_ZRTP
-	zrtp_down(zrtp_global);
+	if (zrtp_on) {
+		zrtp_down(zrtp_global);
+	}
 #endif
 	crypto_kernel_shutdown();