"lookup-only" permission on a folder breaks communication with server. (IMAP error reported by server.)

Steps to reproduce

1. Set permissions to l (lookup only) on a single folder (on an Cyrus IMAP Server)
2. No folders and no mails are shown

Expected behaviour

should show folders and emails, even if there is one folder with only lookup permissions.

if there are no read permissions on a listed folder nextcloud should not disconnect, but move on to the next folder.

Actual behaviour

everything keeps blank, showing the message "loading accounts" forever, on top it shows "unknown Error".
the problem persists if the folder is not subscribed at all.

it seems like the mail client issues a STATUS request on the mentioned folder, the server answers with "no permission" and nextcloud issues a logout.

Error

Horde_Imap_Client_Exception_ServerResponse: IMAP error reported by server.
  at Horde_Imap_Client_Socket::_getLine
     /net/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Socket.php, line 4302
  at Horde_Imap_Client_Socket::_sendCmdChunk
     /net/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Socket.php, line 4230
  at Horde_Imap_Client_Socket::_sendCmd
     /net/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Socket.php, line 1751
  at Horde_Imap_Client_Socket::_status
     /net/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Base.php, line 1728
  at Horde_Imap_Client_Base::status
     /net/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Base.php, line 4033
  at Horde_Imap_Client_Base::_syncStatus
     /net/www/nextcloud/apps/mail/vendor/pear-pear.horde.org/Horde_Imap_Client/Horde/Imap/Client/Base.php, line 3585
  at Horde_Imap_Client_Base::getSyncToken
     /net/www/nextcloud/apps/mail/lib/IMAP/FolderMapper.php, line 65
  at OCA\Mail\IMAP\FolderMapper::getFolders
     /net/www/nextcloud/apps/mail/lib/Service/MailManager.php, line 84
  at OCA\Mail\Service\MailManager::getFolders
     /net/www/nextcloud/apps/mail/lib/Controller/FoldersController.php, line 72
  at OCA\Mail\Controller\FoldersController::index
  at call_user_func_array
     /net/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php, line 161
  at OC\AppFramework\Http\Dispatcher::executeController
     /net/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php, line 91
  at OC\AppFramework\Http\Dispatcher::dispatch
     /net/www/nextcloud/lib/private/AppFramework/App.php, line 115
  at OC\AppFramework\App::main
     /net/www/nextcloud/lib/private/AppFramework/Routing/RouteActionHandler.php, line 47
  at OC\AppFramework\Routing\RouteActionHandler::__invoke
  at call_user_func
     /net/www/nextcloud/lib/private/Route/Router.php, line 297
  at OC\Route\Router::match
     /net/www/nextcloud/lib/base.php, line 999
  at OC::handleRequest
     /net/www/nextcloud/index.php, line 42

conversation nextcloud< - >cyrus:

<1528817613<31 STATUS "Projekte.082.08292 AAA Blabla" (MESSAGES UIDNEXT UIDVALIDITY HIGHESTMODSEQ)
>1528817613>31 NO Permission denied
<1528817613<32 LOGOUT
>1528817613>* BYE LOGOUT received
32 OK Completed

when changing the folders permisson to e.g. lrswipcda everything works fine.

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Start in apps/mail/lib/IMAP/FolderMapper.php, following the STATUS failure through MailManager::getFolders and FoldersController::index. Reproduce the Cyrus IMAP lookup-only case and inspect how the Horde IMAP error is handled. Done means a permission-denied STATUS response does not log out or leave the account loading forever, while other folders remain available.