"files" widget allows to download only the first file, always

To reproduce:

• Have a File document
• Go to the "Files" tab
• Upload 2 documents
• Click the "Store uploaded files" button
• Now, in the list, click the second document: It downloads the first one (but with the correct file name, the file name of the second one).

If you look at the link, you can see that it always use the first file (.../files:files/0/file/...). This is because - I think - the "document_files_edit.xhtml" widget uses model.rowIndex in the loop while it looks like this variable is not set in this context.

So, basically, you can download only the first file stored in the files:files schema, hence "Critical".

Notice: If in the widget, you replace model.rowIndex with counter.count - 1, all is good.

Tested on 6.0HF12 and 7.2 (not on snapshot)