Merge pull request #5853 from ian-r-rose/clear-busy-on-session-disposal

When a session is disposed, also unset any busy status.

packages/apputils/src/clientsession.tsx

@@ -368,6 +368,10 @@ export class ClientSession implements IClientSession {
     if (this._dialog) {
       this._dialog.dispose();
     }
+    if (this._busyDisposable) {
+      this._busyDisposable.dispose();
+      this._busyDisposable = null;
+    }
     Signal.clearData(this);
   }