GThreadedResolver: set an error if no records could be found

It is possible that the upstream servers return something, but
we then filter all results because they are of the wrong type.
In that case the API and subsequent GTask calls expect a GError
to be set.

https://bugzilla.gnome.org/show_bug.cgi?id=696857

gio/gthreadedresolver.c

@@ -472,6 +472,14 @@ g_resolver_records_from_res_query (const gchar      *rrname,
         records = g_list_prepend (records, record);
     }
 
+  if (records == NULL)
+    {
+      g_set_error (error, G_RESOLVER_ERROR, G_RESOLVER_ERROR_NOT_FOUND,
+                   _("No DNS record of the requested type for '%s'"), rrname);
+
+      return NULL;
+    }
+  else
     return records;
 }
 
@@ -616,7 +624,15 @@ g_resolver_records_from_DnsQuery (const gchar  *rrname,
         records = g_list_prepend (records, g_variant_ref_sink (record));
     }
 
-  return records;
+  if (records == NULL)
+    {
+      g_set_error (error, G_RESOLVER_ERROR, G_RESOLVER_ERROR_NOT_FOUND,
+                   _("No DNS record of the requested type for '%s'"), rrname);
+
+      return NULL;
+    }
+  else
+    return records;
 }
 
 #endif