bug#33073: 27.0.50; Fatal error when comparing threads with 'equal'

[Eli Zaretskii]

> From: Gemini Lasswell <gazally@runbox.com>
> Date: Tue, 16 Oct 2018 21:58:20 -0700
> 
> When Emacs is configured with assertions, it fails at one when using
> 'equal' to compare main-thread to another thread.  The configure flags
> which I am using are:
> 
>    --enable-checking=yes,glyphs --enable-check-lisp-object-type
> 
> To reproduce:
> 
> >From emacs -Q, enter the following code into *scratch* and
> then M-x eval-buffer RET:
> 
> (defun my-func () (while t (sleep-for 10)))
> (setq my-t (make-thread 'my-func))
> (equal main-thread my-t) 
> 
> Result:
> 
> lisp.h:1548: Emacs fatal error: assertion failed: 0 <= size

Thanks, should be fixed now.