[BUGFIX] Avoid method calls on null with use of null safe operators

`FrontendUtility::getCurrentPageIdentifier()` and
`FrontendUtility::getSysLanguageUid()` received a guard clause a while ago
to prevent calling `getAttribute()` on a null request.

While this solves issues with a nullable request, there are still
potential issues with calling a method on a null return value of
`getAttribute()`

The use of null-safe operators resolve this issue and make the guard
clauses superfluous.

Fixes: #1358

Author: alexanderschnitzler

Classes/Utility/FrontendUtility.php

@@ -37,21 +37,15 @@ public static function getStoragePage(int $pid = 0): int
      */
     public static function getCurrentPageIdentifier(): int
     {
-        if (self::getRequest() !== null) {
-            return self::getRequest()->getAttribute('frontend.page.information')->getId() ?? 0;
-        }
-        return 0;
+        return self::getRequest()?->getAttribute('frontend.page.information')?->getId() ?? 0;
     }
 
     /**
      * Get configured frontend language
      */
     public static function getSysLanguageUid(): int
     {
-        if (self::getRequest() !== null) {
-            return self::getRequest()->getAttribute('language')->getLanguageId();
-        }
-        return 0;
+        return self::getRequest()?->getAttribute('language')?->getLanguageId() ?? 0;
     }
 
     public static function getPluginName(): string