[m-rev.] for post-commit review: fix Volker's bug

[Peter Wang]

On Sun, 13 Aug 2023 20:38:15 +1000 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> Add inst_lookup_debug, and use it to fix a bug.
> 
> compiler/inst_lookup.m:
>     Add inst_lookup_debug, a new version of the inst_lookup predicate
>     intended to debug problems with inst names. It can recognize and report
>     without crashing two kinds of problems with inst names:
> 
>     - unknown inst names, situations in which an inst name identifies
>       an entry in an inst table that indicates that an operation on insts
>       has begun but has not yet completed, which is a problem if all such
>       operations are supposed to have completed, abd
> 
>     - missing inst names, situations in which an inst name *should* identify
>       an entry in an inst table, but that entry does not exist. In such cases,
>       the inst name is effectively a form of dangling pointer.
> 
>     It reports both kinds of problems by return user insts of a special form
>     that another predicate can recognize, and which contain all the info
>     available about the error.
> 

That looks fine.

Peter