python: call empty eval workaround before auto-load of scripts (issue #2046, issue #2126)

This should definitely fix the crash with Python 3.12, even when scripts are
auto-loaded (the previous fix was working only when the scripts are loaded
manually).

src/plugins/plugin-script.h

@@ -122,6 +122,7 @@ struct t_plugin_script_data
     void (*callback_load_file) (void *data, const char *filename);
 
     /* functions */
+    void (*init_before_autoload) ();
     void (*unload_all) ();
 };