bug#27761: Crash while using proof-general/company-coq on OS X

[Eli Zaretskii]

> From: Денис Редозубов <denis.redozubov@gmail.com>
> Date: Thu, 20 Jul 2017 16:06:55 -0400
> Cc: "Charles A. Roelli" <charles@aurox.ch>, 27761@debbugs.gnu.org
> 
> We were able to determine with John it is definitely an infinite
> loop

Judging by the backtrace, it's not an infinite loop, it's infinite
recursion, which eventually blows up the run-time stack and causes the
segfault.

There's only one place where get_next_display_element calls itself.