[PATCH] output/alert: fix alert index access for verdict

[PATCH] output/alert: fix alert index access for verdict

The engine uses p.alerts.cnt as an index to access the packet alert that
has the `pass` action for the verdict.
For IDS/IPS mode, a `pass` will always be the last signature in the
alert queue. However, that position could be either `p.alerts.cnt` or
`p.alerts.cnt-1`, depending on whether the `pass` rule has the `alert`
keyword or not.
This patch fix corner-case scenarios of:
- accessing an index out of boundaries
- off-by-one access
Without changing how the engine increments the alerts.cnt, as this is
used in many places, and would be a more invasive change.
It checks the two different scenarios, plus the case when there is only
a single match as a silent `pass` rule.

Bug #8021
Bug #7630

Origin: upstream, https://github.com/OISF/suricata/commit/5d6c24cc2ce6a390c0956b7ecb2c5efc47e72abc.patch
Bug: https://redmine.openinfosecfoundation.org/issues/8021
Subject: Upstream fix for CVE-2025-64330

Gbp-Pq: Name CVE-2025-64330.patch