message: Protect the command palette against being paged with no items
  Fixes two crashes amounting to 14% of our crash burden in Simulated
  Selfhost. I can't reproduce this organically, but I was able to do so by
  forcing the command palette to be empty.
diff: @@ -164,12 +164,17 @@ namespace winrt::TerminalApp::implementation
  // - the approximate number of items visible in the list (in other words the size of the page)
  uint32_t CommandPalette::_getNumVisibleItems()
  {
  - const auto container = _filteredActionsView().ContainerFromIndex(0);
  - const auto item = container.try_as<winrt::Windows::UI::Xaml::Controls::ListViewItem>();
  + if (const auto container = _filteredActionsView().ContainerFromIndex(0))
  + {
  + if (const auto item = container.try_as<winrt::Windows::UI::Xaml::Controls::ListViewItem>())
  + {
  const auto itemHeight = ::base::saturated_cast<int>(item.ActualHeight());
  const auto listHeight = ::base::saturated_cast<int>(_filteredActionsView().ActualHeight());
  return listHeight / itemHeight;
  }
  + }
  + return 0;
  + }
  // Method Description:
  // - Scrolls the focus one page up the list of commands.
  