[BUGFIX] Em: Get preconfigured distribution causes warning

This patch adds an early return for empty file name which happens if an
extension isn't installed.

Resolves: #53641
Releases: 6.2
Change-Id: I1cc3605bf5cddfd4e83c363b974a83d20172d0ce
Reviewed-on: https://review.typo3.org/25401
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter

typo3/sysext/core/Classes/Resource/ResourceFactory.php

@@ -434,6 +434,9 @@ class ResourceFactory implements \TYPO3\CMS\Core\SingletonInterface {
 				return $this->getObjectFromCombinedIdentifier($input);
 			} elseif ($prefix == 'EXT') {
 				$input = GeneralUtility::getFileAbsFileName($input);
+				if (empty($input)) {
+					return NULL;
+				}
 				$input = PathUtility::getRelativePath(PATH_site, dirname($input)) . basename($input);
 				return $this->getFileObjectFromCombinedIdentifier($input);
 			} else {