Fix data not being loaded in MRVA results panel

When the MRVA results panel is closed (so the panel gets disposed) and
opened again, it would not load the MRVA data (such as whether a query
has already been downloaded). This fixes it by also resetting the
internal state of whether the panel is loaded when the panel is
disposed.

extensions/ql-vscode/src/remote-queries/remote-queries-interface.ts

@@ -125,6 +125,7 @@ export class RemoteQueriesInterfaceManager {
         () => {
           this.panel = undefined;
           this.currentQueryId = undefined;
+          this.panelLoaded = false;
         },
         null,
         ctx.subscriptions