[Geary] Prefetch period not working for INBOX

[Ricardo Bugalho <rbugalho gmail com>]

Hi,

from my testing, the prefetch_period_days does not work for INBOX.
This is annoying, I want to prefetch all my e-mail, so I can run search
es.

As far as I could, I've traced the problem down to this condition in
send_all:

    if (imap_folder.get_open_state() != Folder.OpenState.CLOSED)
                continue;

https://github.com/GNOME/geary/blob/master/src/engine/imap-engine/imap-
engine-account-synchronizer.vala#L151

INBOX is always open and thus is never sent to process_queue_async.

I've tried removing that condition and it _seems_ to work OK.
> From the comment in that block, it's not clear whether that condition
is just a performance optimization or it there's a possible consistency
issue lurking.

Ricardo