bug#42981: void function next-error-found

[Juri Linkov]

>> I'm using Emacs 26.3 again, and while testing project-search, I noticed
>> that an error is signalled by Xref (1.0.2) use of the function
>> next-error-found, that hasn't been defined as of 26.3. As Xref promises
>> compatibility with 26.3, it seems that next-error-found should be
>> replaced with something more backwards compatible.
>
> Thanks for another important find.
>
> Juri, do you remember what we should call/do instead in Emacs 26?

Hmm, AFAIR there was nothing before adding next-error-found
for Emacs 27 in 0c9e3df3c2.  So you could just make its call
conditional, or copy the current body of next-error-found,
removing some new variables like next-error-found-function,
or just use (setq next-error-last-buffer (or from-buffer (current-buffer)))