[BUGFIX] Use correct fallback types in ImageDimension

Replace wrong null fallback for "width" and "height"
with empty string and also cast the values before
passing to GraphicalFunctions->getImageScale()
which expects them to be string.

Resolves: #97952
Releases: main, 11.5
Change-Id: I80174038e54ce41dfbde5e5e35339b0a7429be4e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75212


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/core/Classes/Imaging/ImageDimension.php

@@ -81,8 +81,8 @@ class ImageDimension
                 $imageDimension->height,
                 $processedFile->getExtension(),
             ],
-            $config['width'] ?? null,
-            $config['height'] ?? null,
+            (string)($config['width'] ?? ''),
+            (string)($config['height'] ?? ''),
             $config
         );
         $imageWidth = $geometryWidth = (int)$result[0];