Fixed issues

• In some cases, PDF files were missing metadata and system-generated tags after upload, which could prevent them from being indexed correctly or appearing in filtered views. PDFs now retain both system-generated information and any custom metadata supplied during upload.
• Improved folder retrieval performance in environments with large numbers of folders.
• Resolved an issue where thumbnails generated for very large images could appear black. 
• Resolved an issue that could prevent download renditions from being generated for very large images.