muc_restore_timeout set to -1 means we want no particular time set, up
to which we request messages. But we should not deliberate request
messages we already have. Hence even if muc_restore_timeout is set
to -1, we should only request up to the last message we received.
Example:
If we receive a message the last message date is now.
If we restart Gajim and join the MUC again, `time.time() - timeout`
will be most likly smaller then when we received the last message
If the timeout is an hour, this would mean that many messages are requested
from the archive which we already received.
So we always want the most current timestamp (MAX).
Philipp Hörist
André Apitzsch