message: Fix crash in PreferencesWindowViewModel
diff: @@ -122,7 +122,7 @@ namespace TogglDesktop.ViewModels
  private void UpdateKnownShortcuts(HotKey previousValue, HotKey newValue, string hotKeyDescription)
  {
  - if (!previousValue.IsNullOrNone())
  + if (!previousValue.IsNullOrNone() && _knownShortcuts.ContainsKey(previousValue))
  {
  if (_knownShortcuts[previousValue] == hotKeyDescription)
  {
  