bug#65631: Xref updates stack in case of error

[Juri Linkov]

X-Debbugs-CC: Dmitry Gutov <dmitry@gutov.dev>

0. emacs -Q
1. move point to any word
2. type 'M-.' (xref-find-definitions)
3. an error is displayed correctly "No definitions found for: This"

But the problem is that an unrecognized word is added to the xref stack.
So the context menu shows "Go Back", and 'M-,' (xref-go-back) goes back
to that word.