datatrails: reloaded trail bugs related to no selected metric (#87344)

* fix: reloaded scene first step topScene

The top scene was not being initialized
when reloading trails, causing it to use
the top scene of whatever was selected
previously.

* fix: select new metric node not reloading right

On reloading trails, any metric node that
was 'green' with a undefined metric due to
clicking on the "select new metric" button,
was reloading with the metric of the step
directly before it (in index order).

public/app/features/trails/DataTrail.tsx

@@ -169,6 +169,11 @@ export class DataTrail extends SceneObjectBase<DataTrailState> {
   public restoreFromHistoryStep(state: DataTrailState) {
     this.disableUrlSync();
 
+    if (!state.topScene && !state.metric) {
+      // If the top scene for an  is missing, correct it.
+      state.topScene = new MetricSelectScene({});
+    }
+
     this.setState(
       sceneUtils.cloneSceneObjectState(state, {
         history: this.state.history,
@@ -213,7 +218,7 @@ export class DataTrail extends SceneObjectBase<DataTrailState> {
       if (this.state.metric !== values.metric) {
         Object.assign(stateUpdate, this.getSceneUpdatesForNewMetricValue(values.metric));
       }
-    } else if (values.metric === null) {
+    } else if (values.metric == null) {
       stateUpdate.metric = undefined;
       stateUpdate.topScene = new MetricSelectScene({});
     }