Add an extra null check to avoid crash when deselecting the item

When the sidebar switches to something else, we're explicitly
setting the data to `null` now to avoid leaving stale data around.
This means that `d.service` can fail when it's removing the stale content.

modules/ui/maproulette_editor.js

@@ -388,7 +388,7 @@ export function uiMapRouletteEditor(context) {
         .text(l10n.t('map_data.layers.maproulette.nearbyTask.title'));
 
       function isSaveDisabled(d) {
-        return (hasAuth && d.service === 'maproulette') ? null : true;
+        return (hasAuth && d?.service === 'maproulette') ? null : true;
       }
     });
   }