[m-rev.] for post-commit review: fix bad mode specializations

[Peter Wang]

On Fri, 26 Feb 2021 17:55:25 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> These were discovered by having them cause compiler aborts
> on a change I am working on :-(
> 
> Zoltan.

> Fix bad mode specializations.
> 
> library/hash_table.m:
> library/stream.string_writer.m:
>     Fix code where a mode specialization (i.e. the specification of
>     a particular input function symbol for an argument) was applied
>     to the wrong argument.

That's fine.

Peter