dataviz: don't render unconfigured gauge cells (#17456)

combo/apps/dataviz/models.py

@@ -47,6 +47,9 @@ class Gauge(CellBase):
     def get_additional_label(self):
         return self.title
 
+    def is_relevant(self, context):
+        return bool(self.data_source)
+
     def get_cell_extra_context(self, context):
         if self.jsonp_data_source:
             data_source_url = get_templated_url(self.data_source)