message: Preventing double-opening of submodule in tabs
  I did not catch this situation when fixing the sidebar : submodules can be opened multiple times in multiple tabs.
  This commit does not change the current behaviour when the Open submodules in tabs option is not checked.
diff: @@ -192,6 +192,15 @@ RepoView *MainWindow::addTab(const QString &path)
  if (path.isEmpty())
  return nullptr;
  + TabWidget *tabs = tabWidget();
  + for (int i = 0; i < tabs->count(); i++) {
  + RepoView *view = static_cast<RepoView *>(tabs->widget(i));
  + if (path == view->repo().workdir().path()) {
  + tabs->setCurrentIndex(i);
  + return view;
  + }
  + }
  +
  git::Repository repo = git::Repository::open(path, true);
  if (!repo.isValid()) {
  warnInvalidRepo(path);
  @@ -207,6 +216,15 @@ RepoView *MainWindow::addTab(const git::Repository &repo)
  QDir dir = repo.workdir();
  RecentRepositories::instance()->add(dir.path());
  + TabWidget *tabs = tabWidget();
  + for (int i = 0; i < tabs->count(); i++) {
  + RepoView *view = static_cast<RepoView *>(tabs->widget(i));
  + if (dir.path() == view->repo().workdir().path()) {
  + tabs->setCurrentIndex(i);
  + return view;
  + }
  + }
  +
  RepoView *view = new RepoView(repo, this);
  git::RepositoryNotifier *notifier = repo.notifier();
  connect(notifier, &git::RepositoryNotifier::referenceUpdated,
  @@ -215,7 +233,6 @@ RepoView *MainWindow::addTab(const git::Repository &repo)
  updateWindowTitle();
  });
  - TabWidget *tabs = tabWidget();
  emit tabs->tabAboutToBeInserted();
  tabs->setCurrentIndex(tabs->addTab(view, dir.dirName()));
  