when $share === false then (int)$share['share_type'] will always be equal to (int)0

which results in following crash:

[root@server nextcloud] sudo -u apache php occ files:scan someuser
The current PHP memory limit is below the recommended value of 512MB.
Starting scan for user 1 out of 1 (someuser)
An unhandled exception has been thrown:
TypeError: Argument 1 passed to OC\OCS\DiscoveryService::discover() must be of the type string, null given, called in /var/www/html/nextcloud/apps/files_sharing/lib/External/Manager.php on line 382 and defined in /var/www/html/nextcloud/lib/private/OCS/DiscoveryService.php:65
Stack trace:
0 /var/www/html/nextcloud/apps/files_sharing/lib/External/Manager.php(382): OC\OCS\DiscoveryService->discover(NULL, 'FEDERATED_SHARI...')
1 /var/www/html/nextcloud/apps/files_sharing/lib/External/Manager.php(527): OCA\Files_Sharing\External\Manager->sendFeedbackToRemote(NULL, NULL, NULL, 'decline')
2 /var/www/html/nextcloud/apps/files_sharing/lib/External/Storage.php(216): OCA\Files_Sharing\External\Manager->removeShare('files/Someth...')
3 [internal function]: OCA\Files_Sharing\External\Storage->checkStorageAvailability()
4 /var/www/html/nextcloud/lib/private/Files/Storage/Wrapper/Wrapper.php(505): call_user_func_array(Array, Array)
5 [internal function]: OC\Files\Storage\Wrapper\Wrapper->__call('checkStorageAva...', Array)
6 /var/www/html/nextcloud/lib/private/Files/Storage/Wrapper/Wrapper.php(505): call_user_func_array(Array, Array)
7 /var/www/html/nextcloud/apps/files_sharing/lib/External/Scanner.php(89): OC\Files\Storage\Wrapper\Wrapper->__call('checkStorageAva...', Array)
8 /var/www/html/nextcloud/apps/files_sharing/lib/External/Scanner.php(44): OCA\Files_Sharing\External\Scanner->scanAll()
9 /var/www/html/nextcloud/lib/private/Files/Utils/Scanner.php(245): OCA\Files_Sharing\External\Scanner->scan('', true, 3)
10 /var/www/html/nextcloud/apps/files/lib/Command/Scan.php(172): OC\Files\Utils\Scanner->scan('/someuser', true, NULL)
11 /var/www/html/nextcloud/apps/files/lib/Command/Scan.php(249): OCA\Files\Command\Scan->scanFiles('someuser', '/someuser', false, Object(Symfony\Component\Console\Output\ConsoleOutput), false, true, false)
12 /var/www/html/nextcloud/3rdparty/symfony/console/Command/Command.php(251): OCA\Files\Command\Scan->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
13 /var/www/html/nextcloud/core/Command/Base.php(162): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
14 /var/www/html/nextcloud/3rdparty/symfony/console/Application.php(946): OC\Core\Command\Base->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
15 /var/www/html/nextcloud/3rdparty/symfony/console/Application.php(248): Symfony\Component\Console\Application->doRunCommand(Object(OCA\Files\Command\Scan), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
16 /var/www/html/nextcloud/3rdparty/symfony/console/Application.php(148): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
17 /var/www/html/nextcloud/lib/private/Console/Application.php(213): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
18 /var/www/html/nextcloud/console.php(96): OC\Console\Application->run()
19 /var/www/html/nextcloud/occ(11): require_once('/var/www/html/n...')
20 {main}[root@server nextcloud]

Signed-off-by: fretn <frederikdelaere+github@gmail.com>