bug#61189: 29.0.60; Strange log-edit-mode M-q bug introduced in 27.1

[Eli Zaretskii <eliz@gnu.org>]

> From: Eric Gillespie <epg@pretzelnet.org>
> Date: Mon, 30 Jan 2023 16:52:01 -0600
> 
> It's an old bug, but it requires such a specific kind of log
> message to trigger that it took me until a few months ago to
> finally hit it!
> 
> To reproduce:
> 0. open modified file under version control
> 1. C-x v v
> 2. Enter the following two-line message (i.e. replace "Summary:" and the rest):
> bork bork bork bork bork bork bork bork bork bork bork bork bork
> bork (e.g. bork) bork bork bork bork bork bork bork bork
> 3. M-q
> 4. M-q
> 
> (I have run with (setq log-edit-hook '(log-edit-show-files)) for a long time
> and that's how I encountered the bug.)
> 
> Expected:
> First M-q fills the paragraph to 70 columns.
> Second does nothing.
> 
> Actual:
> First M-q fills the paragraph to 70 columns.
> Second moves one bork back from line one to line two, adds a colon, and
> deletes the sapce before the opening parenthesis, resulting in:
> 
> bork bork bork bork bork bork bork bork bork bork bork bork bork
> bork:(e.g. bork) bork bork bork bork bork bork bork bork

It's because of the parenthesized "(e.g. bork)" thingy.