bug#35702: xref revert-buffer

[Juri Linkov]

I tried to use project-find-regexp more often than rgrep,
but xref misses an important feature: typing 'g' in the
*xref* buffer fails with this error:

Debugger entered--Lisp error: (error "Buffer does not seem to be associated 
with any file")
  signal(error ("Buffer does not seem to be associated with any file"))
  error("Buffer does not seem to be associated with any file")
  revert-buffer--default(t nil)
  revert-buffer(t)
  funcall-interactively(revert-buffer t)
  call-interactively(revert-buffer nil nil)
  command-execute(revert-buffer)