fix: catch error if no GTK theme is available (headless installs)

dzgui/views/base.py

@@ -323,8 +323,12 @@ class App(Gtk.Application):
 
 MainController = Controller()
 
+try:
     theme = Gtk.IconTheme.get_default()
     icons = theme.list_icons(None)
     if STEAM_ICON not in icons:
         logger.warn(strings.steam_icon_missing)
         warnings.warn(strings.steam_icon_missing, stacklevel=2)
+except Exception as e:
+    logger.warning(e)
+    warnings.warn(strings.gtk_theme_missing, stacklevel=2)