[gimp] gir: Mark gimp_dialog_new() parent nullable

[Niels De Graef <nielsdg src gnome org>]

commit 97fcc8ca0f10ce5c41a23df95ca93132251267f9
Author: Niels De Graef <niels degraef barco com>
Date:   Tue May 5 19:14:58 2020 +0200

    gir: Mark gimp_dialog_new() parent nullable

 libgimpwidgets/gimpdialog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/libgimpwidgets/gimpdialog.c b/libgimpwidgets/gimpdialog.c
index 10090ff6c5..d121f3839d 100644
--- a/libgimpwidgets/gimpdialog.c
+++ b/libgimpwidgets/gimpdialog.c
@@ -351,7 +351,7 @@ gimp_dialog_response (GtkDialog *dialog,
  *                gtk_window_set_title().
  * @role:         The dialog's @role which will be set with
  *                gtk_window_set_role().
- * @parent:       The @parent widget of this dialog.
+ * @parent: (nullable): The @parent widget of this dialog.
  * @flags:        The @flags (see the #GtkDialog documentation).
  * @help_func:    The function which will be called if the user presses "F1".
  * @help_id:      The help_id which will be passed to @help_func.