Make sure we respect log message order

When we are logging something and the logger hasn't been initialized, the messages are deferred and flushed by a shutdown handler. However, when we initialize a session, we set the track ID in the logger, effectively initializing it with everything we need. When we log something and then load the session (or create it), any subsequent logs will be dumped, but the deferred logs will wait until shutdown, changing the order in which they were emitted.

This patch makes sure we flush the deferred logs as soon as we have a track ID (can either be set manually or by, most typically, loading a session). That way, we get those logs out as soon as we can, and subsequent logs entries will be dumped afterwards, keeping their relative order.

This closes #1107