Fix: Fix the fallback filter for alerts with no compose filter

An empty filter was used when the alert had no filter causing an
incomplete report when the alert was triggered manually.

src/manage_sql.c

@@ -12155,7 +12155,7 @@ generate_alert_filter_get (alert_t alert, const get_data_t *base_get_data,
   else
     {
       (*alert_filter_get)->filt_id = NULL;
-      (*alert_filter_get)->filter = g_strdup("");
+      (*alert_filter_get)->filter = base_get_data->filter;
     }
 
   /* Adjust filter for report composer.