Await SessionInit message after ClientLoginAck before sending heartbeat
Await SessionInit message after ClientLoginAck before sending heartbeat

We have to wait for SessionInit before sending a HeartBeatRequest,
otherwise it will be ignored.
This did not trigger with legacy PHP versions because switching test
cases tends to be slow and we implicitly received the message.
PHP 7 is way faster and we better be safe than sorry here.
clue/php-quassel-react