bug#25599: Why edit markers after insert?

[npostavs]

Dmitry Gutov <dgutov@yandex.ru> writes:

> On 09.03.2017 21:39, nitish chandra wrote:
>> The problem is being caused by insert invalidating some of the
>> markers. So before adjusting the markers, we can check if the marker
>> is valid or not. Following is a patch that does this.
>
> Thanks, Nitish. The patch works for me.
>
> Could someone else more familiar with undo give a second opinion, please?

Not that I'm very familiar with the undo code, but the patch seems
obviously correct to me.

+               ;; insert might have invalidated some of the
+               ;; markers. We update only the currently valid
+               ;; markers. See bug#25599

I would augment the comment to specifically mention modification hooks
though (missing double spacing too).