Fix download of preview after file is attached to a document in Web UI

When attaching a file to a document, the preview is downloaded twice and 2 downloaded the document audit entries are added to the document's history.

How to reproduce:

• create a File document in a workspace
• click on Upload main file to attach a file and attach a file of type XML, or TXT, or an image (more file types to come)

Expected result: document's history contains only one downloaded the document audit entry (download of preview)
Actual result: document's history contains 2 downloaded the document audit entries

This issue does not happen when the file attached is a PDF.