Bugfix: Close session properly if activation failed

[Maddin-619]

At the moment if the session activation failed the session dosn't get closed. Depending on the server session timeout there can accumulate lots of danggling sessions.

To close the session after a activation failure the session must be set before calling the Close function.

[magiconair]

Thank you! I've refactored the change to make closing the session explicit and not just a side effect of setting the session. However, we still call setSession in the ActivateSession handler and there is a side-effect here. Question is at which point should the session variable contain a valid value. After creation or after activation? I'll merge it and release a v0.3.16 shortly together with your other fix.

[magiconair]

This will go into v0.4.0

[Maddin-619]

@magiconair In the current version the bug occurs again. A good PR should have include some tests, damn it. Sorry about that.
It's basically the same problem as the last time: If ActivateSession fails, the session is not stored in the atomic variable and therefore cannot be closed. Are you good if i submit another PR? If yes do you prefer the explicit way again?