commit acd6b4b0 ("simplify/fix recursive maildir listing") argued that
listing INBOX when it is encountered while listing Path would be
unnecessary, as the caller would list it separately anyway if requested.
however, it is actually documented that Patterns will implicitly match
INBOX nested into Path. so revert that commit.
REFMAIL: 20240818002409.4c918eb4@inari
tell explicitly that the box cannot be opened _any more_, so it's clear
that Delete, rather than Create, would apply.
fwiw, it would be preferable to actually differentiate between absent
mailboxes and ones that fail to open for other reasons. but
unfortunately, IMAP doesn't report the difference (gmail has a
non-standard [NONEXISTENT] response code, though).