bug#34179: 27.0.50; message hangs when buffer with process visible

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 24 Jan 2019 21:21:48 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 34179@debbugs.gnu.org
> 
> Here's the Lisp backtrace:
> 
>   "select-window" (0x82a508)
>   "window-max-chars-per-line" (0x82aae0)
>   "window-adjust-process-window-size" (0x82b0a0)
>   "window-adjust-process-window-size-smallest" (0x82b618)
>   "window--adjust-process-windows" (0x82bbc0)
>   "redisplay_internal (C function)" (0x0)
>   "message" (0x82cdb0)
>   "progn" (0x82cff8)
>   "if" (0x82d198)
>   "let*" (0x82d3c8)
>   "catch" (0x82d608)
>   "fracy-display-frame-list" (0x82d7c0)
>   "if" (0x82dac8)
>   "fracy-flash-window" (0x82dc80)
>   "let" (0x82e018)
>   "ad-Advice-handle-switch-frame" (0x82e4a0)
>   "apply" (0x82e498)
>   "handle-switch-frame" (0x82ebe0)
>   "funcall-interactively" (0x82ebd8)
>   "call-interactively" (0x82f030)
>   "command-execute" (0x82f628)
> 
> The C portion of the backtrace below selec t-window is this:
> 
>   #0  redisplay_other_windows () at xdisp.c:597
>   #1  0x010aa09e in select_window (window=XIL(0xa000000006919aa0),
>       norecord=XIL(0x3d36a14), inhibit_point_swap=false) at window.c:540
>   #2  0x010aa62a in Fselect_window (window=XIL(0xa000000006919aa0),
>       norecord=XIL(0x3d36a14)) at window.c:628

To clarify: these backtraces show where windows_or_buffers_changed is
being set to the value of 2, which causes us to retry redisplay.  It
is a direct consequence of the fact that window-max-chars-per-line
calls select-window.