gtk: Allow the create-context signal for GLArea to return null
The signal should return None if creating the context fails. Optionally set
an error message with GLAreaExt::set_error.
@@ -813,6 +813,10 @@ module_name = "gl_area"
[[object.signal]]
pattern = "render"
inhibit = true
+ [[object.signal]]
+ name = "create-context"
+ [object.signal.return]
+ nullable = true
[[object]]
name = "Gtk.Grid"
