bug#64516: [PATCH] docview: Only enable imenu when supported

[Basil L. Contovounesios]

> diff --git a/lisp/doc-view.el b/lisp/doc-view.el
> index b14655fb274..847601872f5 100644
> --- a/lisp/doc-view.el
> +++ b/lisp/doc-view.el
> @@ -147,6 +147,8 @@
[...]
> +          (unless (= 0 (call-process "mutool" nil (current-buffer) nil 
> "show" fn "outline"))
> +            (imenu-unavailable-error "Unable to create imenu index using 
> `mutool'"))

Is call-process guaranteed to return a number?
Would eq/l be more suitable than =?

[ The same also appears in doc-view--revert-buffer. ]

Thanks,
-- 
Basil