I have a font initialization in my init file.  Reduced to a minimum
example it does stuff like this:

    (mapc
     (lambda (frame)
       (set-fontset-font nil ?a "sans-serif" frame))
     (frame-list))

This crashes when called from "emacsclient -a '' -c".

As a recipe:

* mkdir /tmp/test
* Copy the above code into /tmp/test/.emacs
* Run HOME=/tmp/test emacsclient -a '' -c

Note that "emacsclient -a emacs -c" does not crash.  There is something
different between "-a ''" and "-a something".

Running gdb on the corresponding core file I get the typescript below.
The problem seems to be in gdb frame #7, where even though there is a
frame reported by frame-list, it does not have a valid fontset and so an
assertion in FRAME_FONTSET(f) fails.

I assume this is not intentional, otherwise how do I prevent the crash?