loader: free error state, when checking the drawable type

Currently we distinguish if the drawable is a window or pixmap by
checking xcb_present_select_input throws an error or not.

Yet, we don't always free the error state returned by xcb.

Cc: Kirill Burtsev <kirill.burtsev@qt.io>
Cc: Boyan Ding <boyan.j.ding@gmail.com>
Fixes: 6bd9ba7d07 ("loader: Add dri3 helper")
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
[Emil: add commit message, fixes tag]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

src/loader/loader_dri3_helper.c

@@ -1509,6 +1509,7 @@ dri3_update_drawable(struct loader_dri3_drawable *draw)
             mtx_unlock(&draw->mtx);
             return false;
          }
+         free(error);
          draw->is_pixmap = true;
          xcb_unregister_for_special_event(draw->conn, draw->special_event);
          draw->special_event = NULL;