[gtk+/gtk-3-18] Add some more missing nullable annotations

[Matthias Clasen <matthiasc src gnome org>]

commit bdfa6ebc2b1a7a39c9c5f360806bf914cffe4532
Author: Timm Bäder <mail baedert org>
Date:   Tue Dec 1 13:40:46 2015 +0100

    Add some more missing nullable annotations

 gtk/gtkgrid.c    |    2 +-
 gtk/gtklistbox.c |    4 ++--
 gtk/gtkwindow.c  |    2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/gtk/gtkgrid.c b/gtk/gtkgrid.c
index 428ce81..ea719c4 100644
--- a/gtk/gtkgrid.c
+++ b/gtk/gtkgrid.c
@@ -1951,7 +1951,7 @@ gtk_grid_attach_next_to (GtkGrid         *grid,
  * Gets the child of @grid whose area covers the grid
  * cell whose upper left corner is at @left, @top.
  *
- * Returns: (transfer none): the child at the given position, or %NULL
+ * Returns: (transfer none) (nullable): the child at the given position, or %NULL
  *
  * Since: 3.2
  */
diff --git a/gtk/gtklistbox.c b/gtk/gtklistbox.c
index 66281f8..2dbe0cd 100644
--- a/gtk/gtklistbox.c
+++ b/gtk/gtklistbox.c
@@ -651,7 +651,7 @@ gtk_list_box_get_selected_row (GtkListBox *box)
  * If @_index is negative or larger than the number of items in the
  * list, %NULL is returned.
  *
- * Returns: (transfer none): the child #GtkWidget or %NULL
+ * Returns: (transfer none) (nullable): the child #GtkWidget or %NULL
  *
  * Since: 3.10
  */
@@ -3324,7 +3324,7 @@ gtk_list_box_row_changed (GtkListBoxRow *row)
  * in a #GtkListBoxUpdateHeaderFunc to see if there is a header
  * set already, and if so to update the state of it.
  *
- * Returns: (transfer none): the current header, or %NULL if none
+ * Returns: (transfer none) (nullable): the current header, or %NULL if none
  *
  * Since: 3.10
  */
diff --git a/gtk/gtkwindow.c b/gtk/gtkwindow.c
index 85d9b8e..a8d2e59 100644
--- a/gtk/gtkwindow.c
+++ b/gtk/gtkwindow.c
@@ -1098,7 +1098,7 @@ gtk_window_class_init (GtkWindowClass *klass)
   /**
    * GtkWindow:set-focus:
    * @window: the window which received the signal
-   * @widget: the newly focused widget (or %NULL for no focus)
+   * @widget: (nullable): the newly focused widget (or %NULL for no focus)
    *
    * This signal is emitted whenever the currently focused widget in
    * this window changes.