Fix: Ensure iso_time uses user TZ when tz_override is empty

[mattmundell]

What

In pl/pgsql function iso_time, convert gvmd.tz_override to NULL when it is the empty string.

Why

This ensures that the user's timezone setting is used (instead of always UTC).

This has two effects:

1. GET commands now correctly return fields like CREATION_TIME in the user's timezone.

time o m m '<get_info type="nvt" filter="sort-reverse=created rows=10 first=1000"/>' > /tmp/info
After:
<creation_time>2023-03-31T11:52:43+02:00</creation_time>
Before:
<creation_time>2023-03-31T09:52:43Z</creation_time>

2. iso_time is much faster

SELECT iso_time (creation_time), iso_time (modification_time) FROM nvts ORDER BY creation_time DESC LIMIT 10 OFFSET 85940;
Before: 11s
After: 3s

In particular this means the GSA SecInfo > NVTs page is much faster when using the pager arrows (going to the end page was 11s and is now 4s for me).

Why is it faster? The broken coalesce was causing the empty string to be passed as zone to iso_time(seconds, zone). I think this was causing the exception to be thrown (and caught), slowing things down.

[github-actions]

Conventional Commits Report

Type	Number
Bug Fixes	1

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