bug#27040: 25.2: fringe click event bug

[Eli Zaretskii]

> From: "Charles A. Roelli" <charles@aurox.ch>
> Date: Sat, 27 May 2017 15:30:00 +0200
> 
> >>    - emacs -q
> >>    - C-h k
> >>    - Click somewhere in the fringe:
> >>
> >>      => Args out of range: "Describe key (or click or menu item):
> >> mouse-1", 0, 64
> >
> > Thanks, fixed.
> 
> Thank you.  Can I ask how you found the source of the error?

By running Emacs under GDB and setting a C-level breakpoint on the
function 'xsignal', through which all the errors are signaled.  That
showed me that Emacs was calling 'substring' on a string shorter than
the 3rd argument of the function.