bug#48408: BUGFIX: window-default-font-height: check for nil string

[Eli Zaretskii]

> Date: Sun, 16 May 2021 00:42:15 -0400
> From: Boruch Baum <boruch_baum@gmx.com>
> Cc: 48408@debbugs.gnu.org
> 
> On 2021-05-16 07:22, Eli Zaretskii wrote:
> >   (terminal-live-p ":0.0")
> 
> on tty frame: nil
> on gui frame: nil
> 
> >   (framep ":0.0")
> 
> on tty frame: nil
> on gui frame: nil
> 
> >   (frames-on-display-list ":0.0")
> 
> on tty frame: (#<frame F152 0x5599a3b27720>)
> on gui frame: (#<frame F152 0x5599a3b27720>)

Thanks.  So you have just one frame in that session, which is a TTY
frame?  I thought it was a session with both GUI and TTY frames, is
that not so?

Anyway, the above probably means we set up frame parameters
incorrectly somewhere.  Hmm...