#10 stopping acceptor/initiator when no session created

[tmm853]

When calling stop() on an acceptor/initiator which hasn't yet created and enabled a session, in Acceptor/Initiator::stop(),

Session* pSession = Session::lookupSession(*i);

returns a zero pointer which causes a crash on next line. The crash can be prevented by checking for zero pointer.

[tmm853]

Acceptor.cpp, Initiator.cpp diff