bug#25883: 25.2; Frequent, but not reproducible, crash on startup

[Eli Zaretskii]

> From: John Wiegley <jwiegley@gmail.com>
> Date: Sun, 26 Feb 2017 11:14:50 -0800
> 
> This only happens when I startup my "alternate" Emacs that I use exclusively
> for ERC, and it only happens maybe once or twice a week (I startup that Emacs
> once a day).  But maybe this stack trace can help give some insight.
> 
> If ever this becomes reliably reproducible, I'll comment further. But what
> might be causing it to happen?

Some serious messup in the display code.  The backtrace basically says
that the display engine became very confused regarding stuff that
comes from buffer and from various display/overlay strings or images.
I haven't seen aborts in bidi_pop_it since I don't remember how long.

I am not familiar enough with ERC support in Emacs -- is it possible
that Emacs tries to display some partial byte stream that includes
incomplete characters, i.e. the byte sequence for some character(s) is
incomplete?