Micro-optimize validation of empty email addresses

[ChristophWurst]

Then we don't have to construct any validators.

Ref #25582 (comment)

[tcitworld]

We could also look for @ since that's required but it's probably not worth it.

[faily-bot]

🤖 beep boop beep 🤖

Here are the logs for the failed build:

Status of 2155: failure

mariadb10.1-php7.3

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 bash tests/drone-run-php-tests.sh || exit 0
=========================
= List of changed files =
=========================
lib/private/Mail/Mailer.php
tests/lib/Mail/MailerTest.php
=========================
PHP files are modified
+ NOCOVERAGE=true TEST_SELECTION=DB ./autotest.sh mariadb
Using PHP executable /usr/bin/php
Using database oc_autotest
Setup environment for mariadb testing on local storage ...
Waiting for MariaDB initialisation ...
...........................................................................................................................................................................................................................................................................................................
[ERROR] Waited 300 seconds, no respons

postgres12-php7.4

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 bash tests/drone-run-php-tests.sh || exit 0
=========================
= List of changed files =
=========================
lib/private/Mail/Mailer.php
tests/lib/Mail/MailerTest.php
=========================
PHP files are modified
+ sleep 10
+ POSTGRES=12 NOCOVERAGE=true TEST_SELECTION=DB ./autotest.sh pgsql
Using PHP executable /usr/bin/php
Using database oc_autotest
Setup environment for pgsql testing on local storage ...
Waiting for Postgres to be available ...
............................................................
[ERROR] Waited 60 seconds for postgres-12, no respons

integration-ratelimiting

• failure block could not be found - most likely this run got canceled

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+ bash tests/drone-run-integration-tests.sh || exit 0
=========================
= List of changed files =
=========================
lib/private/Mail/Mailer.php
tests/lib/Mail/MailerTest.php
=========================
PHP files are modified
+ ./occ maintenance:install --admin-pass=admin --data-dir=/dev/shm/nc_int
Nextcloud was successfully installed
+ ./occ config:system:set redis host --value=cache
System config value redis => host set to string cache
+ ./occ config:system:set redis port --value=6379 --type=integer
System config value redis => port set to integer 6379
+ ./occ config:system:set redis timeout --value=0 --type=integer
System config value redis => timeout set to integer 0
+ ./occ config:system:set --type string --value "\OC\Memcache\Redis" memcache.local
System config value memcache.local set to string \OC\Memcache\Redis
+ ./occ config:system:set --type string --value "\OC\Memcache\Redis" memcache.distributed
PHP Warning:  Redis::connect(): php_network_getaddresses: getaddrinfo failed: Name or service not known in /drone/src/lib/private/RedisFactory.php on line 92
An unhandled exception has been thrown:
RedisException: Redis server went away in /drone/src/lib/private/Memcache/Redis.php:55
Stack trace:
#0 /drone/src/lib/private/Memcache/Redis.php(55): Redis->get('e2eedb157073b5e...')
#1 /drone/src/lib/private/App/InfoParser.php(60): OC\Memcache\Redis->get('/drone/src/apps...')
#2 /drone/src/lib/private/App/AppManager.php(511): OC\App\InfoParser->parse('/drone/src/apps...')
#3 /drone/src/lib/private/legacy/OC_App.php(589): OC\App\AppManager->getAppInfo('files', false, NULL)
#4 /drone/src/lib/private/AppFramework/App.php(70): OC_App::getAppInfo('files')
#5 /drone/src/lib/private/legacy/OC_App.php(270): OC\AppFramework\App::buildAppNamespace('files')
#6 /drone/src/lib/private/AppFramework/Bootstrap/Coordinator.php(108): OC_App::registerAutoloading('files', '/drone/src/apps...')
#7 /drone/src/lib/private/AppFramework/Bootstrap/Coordinator.php(82): OC\AppFramework\Bootstrap\Coordinator->registerApps(Array)
#8 /drone/src/lib/base.php(634): OC\AppFramework\Bootstrap\Coordinator->runInitialRegistration()
#9 /drone/src/lib/base.php(1076): OC::init()
#10 /drone/src/console.php(49): require_once('/drone/src/lib/...')
#11 /drone/src/occ(11): require_once('/drone/src/cons...')