[BUGFIX] Fix possible warning

Fixes: https://forge.typo3.org/issues/65827

Classes/Loader.php

@@ -95,7 +95,7 @@ class Loader {
 		/** @var $locales \TYPO3\CMS\Core\Localization\Locales */
 		$locales = GeneralUtility::makeInstance('\TYPO3\CMS\Core\Localization\Locales');
 		$locales->initialize();
-		$isoArray = $locales->getIsoMapping();
+		$isoArray = (array) $locales->getIsoMapping();
 
 		if (array_key_exists($languageKey, $isoArray)) {
 			$languageKey = $isoArray[$languageKey];