bug#65631: Xref updates stack in case of error

[Juri Linkov]

>> 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.
>
> FWIW, I'm not sure this is necessarily a bug.  It looks like a bug in
> your case, because you deliberately tricked Xref into using a word
> that is definitely not a program symbol.  But that is not the case in
> a more reasonable situation, where point is on a symbol, but for some
> reason the symbol's definition is not found, e.g., because the TAGS
> table needs to be regenerated.

In case of error, point doesn't move.  So there is no need to go back.