stock images: copy uploaded file if image width is smaller than target width, fixes #4377

Closes #4377

Merge request studip/studip!3183

lib/classes/StockImages/Scaler.php

@@ -20,13 +20,14 @@ final class Scaler
     {
         $image = $this->createImage($stockImage);
         $width = imagesx($image);
+
         if ($width < $targetWidth) {
-            return false;
+            $scaledImage = $image;
+        } else {
+            $scaledImage = imagescale($image, $targetWidth);
+            imagedestroy($image);
         }
 
-        $scaledImage = imagescale($image, $targetWidth);
-        imagedestroy($image);
-
         return $this->storeImage($stockImage, $scaledImage, $sizeName);
     }