Fix broken STARTTLS

It appears that `STARTTLS` support is currently broken for me.  After a bit of digging, this appears to be due to 2 issues.  The first is that the connection is prematurely closed for servers which report `LOGINDISABLED` before `STARTTLS`.  The second is that `node-imap` stops reading data from the connection after `STARTTLS`.  This patch set fixes both issues (for me).