altTab: Use more appropriate fallback icon
'icon-missing' is not an actual icon name. It somewhat works because an invalid icon name will fallback to the correct 'image-missing', however for apps the generic app icon is a better fallback.
'icon-missing' is not an actual icon name. It somewhat works because an invalid icon name will fallback to the correct 'image-missing', however for apps the generic app icon is a better fallback.