bug#42981: void function next-error-found

[Philip K.]

Hi,

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.

-- 
        Philip K.