simplify the code

Author: Cyperghost

wcfsetup/install/files/lib/system/cache/eager/data/LanguageCacheData.class.php

@@ -61,16 +61,19 @@ public function getLanguageCategory(string $categoryName): ?LanguageCategory
     public function getLanguageCategoryByID(int $languageCategoryID): ?LanguageCategory
     {
         $categoryName = $this->categoryIDs[$languageCategoryID] ?? null;
+        if ($categoryName === null) {
+            return null;
+        }
 
-        return $this->categories[$categoryName] ?? null;
+        return $this->getLanguageCategory($categoryName);
     }
 
     /**
      * Returns `true` if the language category with the given category name exists.
      */
     public function languageCategoryExists(string $categoryName): bool
     {
-        return isset($this->categories[$categoryName]);
+        return \array_key_exists($categoryName, $this->categories);
     }
 
     /**