[gtk+/gtk-3-22] Fix some nullable Returns annotations

[Daniel Boles <dboles src gnome org>]

commit 9af612d314199d8250c4c3c4dec1628a5a862c45
Author: Daniel Boles <dboles src gnome org>
Date:   Thu Aug 3 20:26:18 2017 +0100

    Fix some nullable Returns annotations
    
    based on reports and patches by Iñaki García Etxebarria:
    
    https://bugzilla.gnome.org/show_bug.cgi?id=781246
    https://bugzilla.gnome.org/show_bug.cgi?id=785423

 gtk/gtkbin.c    |    3 ++-
 gtk/gtkwidget.c |    5 +++--
 2 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkbin.c b/gtk/gtkbin.c
index 9d7a050..be57027 100644
--- a/gtk/gtkbin.c
+++ b/gtk/gtkbin.c
@@ -321,7 +321,8 @@ gtk_bin_size_allocate (GtkWidget     *widget,
  * no child widget. The returned widget does not have a reference
  * added, so you do not need to unref it.
  *
- * Returns: (transfer none): pointer to child of the #GtkBin
+ * Returns: (transfer none) (nullable): the child of @bin, or %NULL if it does
+ * not have a child.
  **/
 GtkWidget*
 gtk_bin_get_child (GtkBin *bin)
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 9649e68..ced572d 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -10658,9 +10658,10 @@ gtk_widget_set_parent_window (GtkWidget *widget,
  * gtk_widget_get_parent_window:
  * @widget: a #GtkWidget.
  *
- * Gets @widget’s parent window.
+ * Gets @widget’s parent window, or %NULL if it does not have one.
  *
- * Returns: (transfer none): the parent window of @widget.
+ * Returns: (transfer none) (nullable): the parent window of @widget, or %NULL
+ * if it does not have a parent window.
  **/
 GdkWindow *
 gtk_widget_get_parent_window (GtkWidget *widget)