freetdm: only handle zt events when FTDM_CHANNEL_EVENT is set

libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c

@@ -1131,7 +1131,6 @@ FIO_SPAN_NEXT_EVENT_FUNCTION(zt_next_event)
 		ftdm_channel_t *fchan = span->channels[i];
 		if (ftdm_test_flag(fchan, FTDM_CHANNEL_EVENT)) {
 			ftdm_clear_flag(fchan, FTDM_CHANNEL_EVENT);
-		}
 			if (ioctl(fchan->sockfd, codes.GETEVENT, &zt_event_id) == -1) {
 				snprintf(span->last_error, sizeof(span->last_error), "%s", strerror(errno));
 				return FTDM_FAIL;
@@ -1152,6 +1151,7 @@ FIO_SPAN_NEXT_EVENT_FUNCTION(zt_next_event)
 			*event = &span->event_header;
 			return FTDM_SUCCESS;
 		}
+	}
 
 	return FTDM_FAIL;
 }