[TASK] Drop redundant condition from TransportFactory

The variable `$port` in the changed code is an array element
from the return value of `GeneralUtility::trimExplode()` with
the `$removeEmptyValues` argument set to `true`. Hence it
is ensured to not be an empty string.

This change should be backported as it otherwise would block
improvements for the type annotations of
`GeneralUtility::trimExplode()`.

Resolves: #101384
Releases: main, 12.4, 11.5
Change-Id: I74ce433495fc3975c11991d21831db0244eacba0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80085
Tested-by: Alexander Schnitzler <git@alexanderschnitzler.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan B�rk <stefan@buerk.tech>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Alexander Schnitzler <git@alexanderschnitzler.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/core/Classes/Mail/TransportFactory.php

@@ -87,7 +87,7 @@ public function get(array $mailSettings): TransportInterface
                 if ($host === '') {
                     throw new Exception('$GLOBALS[\'TYPO3_CONF_VARS\'][\'MAIL\'][\'transport_smtp_server\'] needs to be set when transport is set to "smtp".', 1291068606);
                 }
-                if ($port === null || $port === '') {
+                if ($port === null) {
                     $port = 25;
                 } else {
                     $port = (int)$port;