core: fix memory leak in case of error

src/gui/gui-bar-window.c

@@ -923,6 +923,7 @@ gui_bar_window_content_get_with_filling (struct t_gui_bar_window *bar_window,
                     if (content)
                         free (content);
                     free (split_items);
+                    free (linear_items);
                     return NULL;
                 }
                 content = content2;