Previously, LoginJob started the SSL negotiation and immediately sent the
CAPABILITY command once it completed, without waiting for the server greeting
first. Some servers don't like this any close the connection with
* BYE out-of-sync data before server greeting

Avoid this by starting the encryption in Session directly, which then starts
LoginJob after the server greeting arrived. Adjust LoginJob for this by
treating an already encrypted connection like a successful negotation, and
avoid handling the encryptionNegotiationResult signal before the job was
started.

BUG: 449184