Socket#onClose(): ensure transport won't stay open.
Socket#onClose(): ensure transport won't stay open.

There are rare error cases when transport could stay open in the background
even if socket is closed, so it is better to always call
`this.transport.close()` in Socket#onClose as it is idempotent and
safe to call multiple times.

sanemat/engine.io-client,socketio/engine.io-client,jskrzypek/engine.io-client,juancancela/engine.io-client,SpainTrain/engine.io-client,socketio/engine.io-client,vedmalex/engine.io-client,nkzawa/engine.io-client,BernhardRode/engine.io-client,julianduque/engine.io-client,gsklee/engine.io-client,Automattic/engine.io-client,socketio/engine.io-client,lwahonen/engine.io-client,AnyPresence/engine.io-client,enounca/engine.io-client,hellpf/engine.io-client,juancarloscancela/engine.io-client