bug#23906: 25.0.95; Undo boundary after process output is not consistent

[Stefan Monnier]

> together in a pure way: It's OK if the handle is simply *not* used.

Indeed, it's perfectly OK.

> And a question: Is there any reason not to write viper-adjust-undo as:

>    (defun viper-adjust-undo ()
>      (when viper--undo-change-group-handle
>        (undo-amalgamate-change-group viper--undo-change-group-handle)
>        (setq viper--undo-change-group-handle nil)))

No really strong reason, no, but it just seems safer to set
viper--undo-change-group-handle to nil before we start with
undo-amalgamate-change-group, in case it signals an error.


        Stefan