Fix a crash if msg_info or msg_info->driver are NULL.
Merge branch 'mailmessage-flush-null-checks'
Parse Gmail's "Too many simultaneous connections" login response.

This is diagnosed as MAILIMAP_ERROR_TOO_MANY_SIMULTANEOUS_CONNECTIONS
(previously was MAILIMAP_ERROR_LOGIN).
Merge branch 'gmail-too-many-simultaneous-connections'