bug#24206: 25.1; Curly quotes generate invalid strings, leading to a segfault

[Dmitry Gutov]

On 08/14/2016 07:54 AM, Paul Eggert wrote:
> Thanks forreporting that, Phil. Ituncovered several bugs in
> substitute-command-keys,some predating the curved-quote changes in Emacs
> 25.

So much for "this is a simple feature that's easy to implement in C".

Could you please at least add some tests corresponding to the fix? 
Instead of just hoping that nobody breaks it later.