bug#15365: 24.3.50; Segfault when calling vc-git-log-edit-toggle-amend

[martin rudalics]

>> So where was Dmitry's cursor?
>
> At PT, whose value was 78.

So PT was not in the window and the fact that it apparently passed the
earlier check (PT < CHARPOS (start)) means that PT was after the end of
the window.  Is that conclusion correct?

> But I probably don't understand what you wanted to ask or tell.

Figure out why row_containing_pos (w, PT, r0, NULL, 0) returned 0.  And
why try_window_id was supposed to abort in this case and why this abort
didn't occur more frequently.

martin