Sequence signature checks later

[SteveSyfuhs]

What's the problem?

11B introduced a new signature type to cover the PAC using the privilege key. This breaks ordering of checks and results in a NRE.

• [X] Bugfix
• [ ] New Feature

What's the solution?

Move the processing of signatures until after the whole PAC is parsed.

• [X] Includes unit tests
• [ ] Requires manual test