If the user supplies an invalid session (as in not on the session
list), it will cause a backtrace, because the setup method from
Msf::PostMixin isn't actually called.
We have thought about implementing this in a new OptSession instead.
But you can't use or even pass framework to option_container.rb, so
this is NOT possible.
The original PR was #3956.
sinn3r
f6f0050f56