degesch: Lua: fix memory leak on load failure

degesch.c

@@ -8845,8 +8845,7 @@ lua_plugin_load (struct app_context *ctx, const char *filename,
 	else
 		return &plugin->super;
 
-	lua_close (L);
-	free (plugin);
+	plugin_destroy (&plugin->super);
 	return NULL;
 }