bug#30937: In `comment-region', C-g doesn't work.

[Alan Mackenzie]

Hello, Emacs.

emacs-26.0.91 -Q
C-x C-f Any largish file.c
C-x h                 ; mark buffer.
C-c C-c               ; comment-region.

This is the sort of thing that can happen by accident.  Depending on the
size of the file.c and the speed of your machine, you've now got a long,
long wait.  C-g doesn't work.  This is a bug.

(The same applies to `uncomment-region'.)

-- 
Alan Mackenzie (Nuremberg, Germany).