IMAP: Ignore empty ENABLED responses when switching mailboxes
Some versions of Cyrus send out extra ENABLED responses. Trojita already
contains code (see bug 329204) for filtering them out in case they look
relevant to CONDSTORE or QRESYNC, but it turns out that sometimes we get
back an empty ENABLED as well.
There is a couple of options here, either to play the guessing game and
add a kludge to silently eat the empty ENABLED to fix this particular
bug, or to change the code to accept any possible ENABLED response while
switching mailboxes.
BUG: 350006
CCBUG: 329204
Upstream-Bug: https://bugzilla.cyrusimap.org/show_bug.cgi?id=3898
Change-Id: I7ce7e663108d5b64a46580fb4aaa57c4cf379445