bug#59137: [PATCH] To minor changes related to overlays

[Stefan Kangas]

Matt Armstrong <matt@rfc20.org> writes:

> The admittedly redundant NULL check done by itree_empty_p does not
> change semantics or cause harm.  mark_overlays in alloc.c is a recursive
> function so it handles NULL itself, hence the NULL check was omitted in
> the original code.

Thanks.

I guess as this is a minor cleanup this should go to master at this point.