Code review comment for lp:~alan-griffiths/mir/fix-1188451

Since Eleni's extra error checking has landed...

/home/dan/bzr/mir/tmp.alan/src/server/frontend/session_mediator.cpp:64:39: error: declaration of ‘virtual mir::frontend::SessionMediator::~SessionMediator()’ has a different exception specifier
In file included from /home/dan/bzr/mir/tmp.alan/src/server/frontend/session_mediator.cpp:19:0:
/home/dan/bzr/mir/tmp.alan/include/server/mir/frontend/session_mediator.h:70:5: error: from previous declaration ‘virtual mir::frontend::SessionMediator::~SessionMediator() noexcept (true)’