s3:param:service - ensure registry shares loaded before home check

Registry shares should be loaded and checked prior to checking home directories. This ensures that an explicitly defined service takes priority over home directories (same behavior as non-registry shares). This is a problem because if a user has a [media] service and a user "media" with a homedir of /var/empty, then attempts to access \server\media will land in /var/empty rather than [media].

https://bugzilla.samba.org/show_bug.cgi?id=14543

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• (optional) This MR is just one part towards a larger feature.
• (optional, if backport required) Bugzilla bug filed and BUG: tag added
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated
• CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code