message: docview: don't open same page twice
diff: @@ -170,6 +170,9 @@ export class DocViewProvider implements Disposable {
  /** Called by the user clicking a link. */
  async open(url?: string) {
  + if (this.currentURL === url) {
  + return;
  + }
  if (url) {
  this.backstack.push(this.currentURL);
  this.forwardstack = [];
  