bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[martin rudalics]

> For `C-h b' it was broken by design because after killing the initial buffer:
>
> 1. C-h b
> 2. click function name link
> 3. kill *scratch*
> 4. click back
>
> clicking on [back] fails with the error "Selecting deleted buffer".

Well, we could handle that more smoothly.  But the principal problem
remains - namely that going back all of a sudden describes different
bindings.

martin