avoid crash when PinMap is missing a warning handler (#12607)

frontend/src/metabase/visualizations/components/PinMap.jsx

@@ -159,8 +159,9 @@ export default class PinMap extends Component {
         t`We filtered out ${filteredRows} row(s) containing null values.`,
       );
     }
-    // $FlowFixMe flow thinks warnings can be undefined
-    onUpdateWarnings(warnings);
+    if (onUpdateWarnings && warnings) {
+      onUpdateWarnings(warnings);
+    }
 
     const bounds = L.latLngBounds(points);