[goocanvas] Let goo_canvas_pointer_grab take NULL

[Alberto Fanjul <albfan src gnome org>]

commit 41ab5ad2817723f00377607beb24894bb237c597
Author: Alexey Sokolov <sokolov google com>
Date:   Mon Nov 2 18:48:00 2020 +0000

    Let goo_canvas_pointer_grab take NULL

 src/goocanvas.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/goocanvas.c b/src/goocanvas.c
index 84478ca..e3477b2 100644
--- a/src/goocanvas.c
+++ b/src/goocanvas.c
@@ -3500,7 +3500,7 @@ goo_canvas_grab_focus (GooCanvas     *canvas,
  * @canvas: a #GooCanvas.
  * @item: the item to grab the pointer for.
  * @event_mask: the events to receive during the grab.
- * @cursor: the cursor to display during the grab, or NULL.
+ * @cursor: (nullable): the cursor to display during the grab, or NULL.
  * @time: the time of the event that lead to the pointer grab. This should
  *  come from the relevant #GdkEvent.
  *