bug#37415: Asserting failure setting frame parameters to non-fixnum values in early-init.el

[Eli Zaretskii]

> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Mon, 16 Sep 2019 00:34:01 +0200
> 
> This is with an empty init.el, and the following early-init.el:
> 
> D:\...\.emacs.d> type early-init.el
> (setq default-frame-alist '((left . (+ 0))))
> 
> D:\...\.emacs.d> emacs.exe
> 
> lisp.h:1231: Emacs fatal error: assertion failed: FIXNUMP (a)

Is this use case important enough to support?  IOW, would just
signaling an error do the job here?  If not, please explain why did
you need to set default-frame-alist in the early-init file.

Thanks.