bug#6690: 24.0.50; tmm-get-keymap is broken

[Drew Adams]

> More information was requested three years ago, but no further
> progress has been made.  Is this bug still present in
> Emacs 24.3?

More precisely, Stefan said:

> Indeed, the code is brittle in this regard.
> I could easily work around the problem by checking `str'
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> before taking its width (concat should work just fine with nil),
> but before I do that, I'd like to make sure the result (which
> would basically treat a nil as equivalent to "") is right...

I have no way to determine that more that he does (and did).

Sorry, it's been 3 years and I don't have anything more to offer
about this.  If you don't want to make the code less brittle and
fix the case where the value is nil, so be it.

Personally, I don't use tmm anyway.  It's possible that I
happened to notice this problem when looking at the code.
Or perhaps I ran into it while experimenting with the code.
I really don't know.