Fix ElDoc's eldoc-documentation-enthusiast strategy

Fix ElDoc's eldoc-documentation-enthusiast strategy

As soon as we get a response from any of the user functions/sources in
eldoc-documentation-functions, we must make sure to call the
display-doc local function, just like in the other strategies.

That is even if that response produced nil, meaning that there's no
doc coming from that source.  Failure to do so when none of the
sources produced non-nil would keep stale documentation displaying.

First reported in https://github.com/joaotavora/eglot/issues/503

* lisp/emacs-lisp/eldoc.el (eldoc--invoke-strategy): Fix
:enthusiast strategy.
(Version): Bump to 1.10.0