Thumbnail preview returns HTTP 500 for high-resolution JPEG images

### Description

When attempting to preview a large high-resolution JPEG image via the ownCloud web interface (public link), the thumbnail generation fails with an HTTP 500 error. The preview page shows "Failed to load" instead of the image.

### Steps to Reproduce

1. Upload a high-resolution JPEG image (12288×8192, ~38MB)
2. Share it via a public link
3. Open the file preview in the web interface

### Expected Behavior

The thumbnail preview should render the image successfully.

### Actual Behavior

The preview page shows "Failed to load [filename]". The browser console shows the thumbnail endpoint returning HTTP 500.

### Environment

- **OCIS version**: 8.0.2+af145c25 (Infinite Scale)
- **Web UI version**: 10.11.0
- **Browser**: Chromium

### Additional Notes

- The image can be downloaded via WebDAV without issues — the problem is specific to thumbnail/preview generation.
- The image is from a Hasselblad L3D-100c camera, JPEG format.
- The thumbnail endpoint returns 500 for all images in this high-resolution set, suggesting the issue may be related to image resolution (12288×8192) or file size (~38MB).