Properly dispose session during logout workflow

TODO:

Add "$this->SessionSet = false;" code in the "\InpSession::Destroy" method.

Motivation:

The "SessionSet" flag is reset in "\Session::Destroy" method, but not in "\InpSession::Destroy" method. Because of this any code, that calls "\kApplication::RemoveVar" method in hooks to the "adm:OnBeforeShutdown" would result in session data removal SQL being executed without SessionKey in it.