fix: fix session event timer stop

[kennethkongiw]

If data is sent to s.sessionEvent after for loop breaks, s.stateTimer.Stop() and s.peerTimer.Stop() would blocked because s.sessionEvent is blocked, the event timer callback would never return.

[kennethkongiw]

Hi @ackleymi,

Would you please review/merge it if you have time?

Tell me if there is something i can do.

Thank you.

[ackleymi]

@robuxto I like this a lot, I would feel much better if I had a test in session_test.go with some behavior verification. You can run go test -v -timeout=15s -count=1 -run SessionSuite as a shortcut to only test stuff you've added.