gdk: add missing nullable annotations
-
For the
gdk_content_(serializer|deserializer)_get_cancellable
: the cancellable seems to be set atgdk_content_(serializer|deserializer)_run
which is called bygdk_content_(serialize|deserialize)_async
that hascancellable
set as nullable -
gdk_event_get_surface
: if you look atgdk_event_get_display
it seems to do a null check & return a null if the surface isn't set -
gdk_x11_surface_get_group
: i'm not very sure about this one but there's a check whether the surface is destroyed.