bug#32975: Emacs 26.1; GTK Warnings

[Robert Pluim]

martin rudalics <rudalics@gmx.at> writes:

>> So I donʼt think we should be calling GTK functions on scrollbars that
>> are not GTK widgets (Iʼm stunned we've never seen this before).
>
> Setting the background color on a GTK build without GTK scroll bars
> seems pretty rare to me.  In addition, one usually has to look at the
> console to see the warnings.
>
>> This
>> fixes it for me. Martin?
>
> Do we want to skip xg_set_widget_bg too?

I can't see a code path where that would get called in the non-toolkit
case, but the code is a twisty maze of similar functions.

Robert