Fix "session_id" parameter for static session IDs in AgaviSessionStorage

[thomasbachem]

No description provided.

[dzuelke]

What problem is this solving? Please provide explanations for PRs and use a few comments in the source code.

[thomasbachem]

The "session_id" setting isn't working at all right now, as the check for session_id() === '' will always lead to false if the "session_id" parameter is provided, as session_id($this->getParameter('session_id')); is called just before the check.

[dzuelke]

There's a lot more broken in that part of the code than just session_id() I think. The whole autostart block never executes IIRC. Is that related?

[thomasbachem]

It's just that the auto_start setting is not used anywhere – but the block gets still executed. Strictly speaking it isn't related, but we should strip that setting from the docblock.