[Core] Fix missing mutex unlock in switch_ivr_dmachine_ping()

src/switch_ivr_async.c

@@ -546,6 +546,7 @@ SWITCH_DECLARE(switch_status_t) switch_ivr_dmachine_ping(switch_ivr_dmachine_t *
 	}
 
 	if (dmachine->pinging) {
+		switch_mutex_unlock(dmachine->mutex);
 		return SWITCH_STATUS_BREAK;
 	}