bug#18547: repeated C-s doesn't wrap back to the top if file is .gz

[Juri Linkov <juri@jurta.org>]

> $ emacs -q directory_that_contains_a_.gz_file
> v on that file. (view mode)
> C-s some_string, C-s C-s C-s C-s C-s ... but then instead of wrapping
> around back to the top, we get
> File not found and directory write-protected
>
> By the way, it happened on a changelog.gz
> file, and the prompt was "Multi I-Search" whatever that means.

It fails because you are using a non-standard file name
"changelog", and not the default "ChangeLog".  You can customize
`change-log-default-name' to "changelog" then isearch will wrap
to the beginning instead of trying to wrap to a non-existent "ChangeLog".

I'm not sure whether we should deduce change-log-name from the
file name of the current buffer (removing possible suffixes
like ".10" from "changelog.10").