[CalDAV] Validate notified emails

[tcitworld]

Some user managed to have some event with this.

PRODID:+//IDN bitfire.at//DAVx5/2.5.1-ose ical4j/2.2.4
[...]
ORGANIZER:mailto:Framagenda

This generates the following:

An unhandled exception has been thrown:
TypeError: idn_to_ascii() expects parameter 1 to be string, null given in /var/www/nextcloud/lib/private/Mail/Message.php:88
Stack trace:
#0 [...]/nextcloud/lib/private/Mail/Message.php(88): idn_to_ascii(NULL, 0, 1)
#1 [...]/nextcloud/lib/private/Mail/Message.php(149): OC\Mail\Message->convertAddresses(Array)
#2 [...]/nextcloud/apps/dav/lib/CalDAV/Reminder/NotificationProvider/EmailProvider.php(122): OC\Mail\Message->setTo(Array)
#3 [...]/nextcloud/apps/dav/lib/CalDAV/Reminder/ReminderService.php(150): OCA\DAV\CalDAV\Reminder\NotificationProvider\EmailProvider->send(Object(Sabre\VObject\Component\VEvent), 'Personal', Array)
#4 [...]/nextcloud/apps/dav/lib/Command/SendEventReminders.php(84): OCA\DAV\CalDAV\Reminder\ReminderService->processReminders()
#5 [...]/nextcloud/apps/bookmarks/vendor/symfony/console/Command/Command.php(255): OCA\DAV\Command\SendEventReminders->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#6 [...]/nextcloud/apps/bookmarks/vendor/symfony/console/Application.php(1009): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#7 [...]/nextcloud/apps/bookmarks/vendor/symfony/console/Application.php(273): Symfony\Component\Console\Application->doRunCommand(Object(OCA\DAV\Command\SendEventReminders), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#8 [...]/nextcloud/apps/bookmarks/vendor/symfony/console/Application.php(149): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#9 [...]/nextcloud/lib/private/Console/Application.php(215): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#10 [...]/nextcloud/console.php(100): OC\Console\Application->run()
#11 [...]/nextcloud/occ(11): require_once('/var/www/nextcl...')
#12 {main}

(unrelated, but quite strange paths with the bookmarks app here)

This makes sure both event's attendees and sharees, as well as event's organizer email addresses, are validated before trying to send them.

[nickvergessen]

I guess we should backport?

[rullzer]

/backport to stable20

[rullzer]

/backport to stable19