[v10.0.x] Graph: Fix bug with showing/hiding the legend (#68829)

Graph: Fix bug with showing/hiding the legend (#68774)

* don't unmount the root when hiding the legend

* update comment

(cherry picked from commit 0b6c5722a5)

Co-authored-by: Ashley Harrison <ashley.harrison@grafana.com>

public/app/plugins/panel/graph/graph.ts

@@ -136,9 +136,14 @@ class GraphElement {
 
     if (!this.panel.legend.show) {
       if (this.legendElem.hasChildNodes()) {
-        this.legendElemRoot.unmount();
+        this.legendElemRoot.render(null);
       }
-      this.renderPanel();
+      // we need to wait for react to finish rendering the legend before we can render the graph
+      // this is a slightly worse version of the `renderCallback` logic we use below
+      // the problem here is there's nothing to pass a `renderCallback` to since we don't want to render the legend at all.
+      setTimeout(() => {
+        this.renderPanel();
+      });
       return;
     }