Thumbnails are not displayed on MyDSpace for WorkspaceItems

[tdonohue]

Describe the bug

On the MyDSpace page, items that are still in the "workspace" never display their thumbnails (even if one exists). You'll always see the "No Thumbnail Available" image.

To Reproduce

Steps to reproduce the behavior:

1. Create a new submission and upload a bitstream which is supported for thumbnails (e.g. image file, PDF, etc)
2. Login as an Admin, and run the "filter-media" script. A thumbnail will be created for the WorkspaceItem you created in step 1.
3. Go back to you MyDSpace page and find the WorkspaceItem. On the MyDSpace page, you'll see "No Thumbnail Available".
4. Click on the "View" button next to that item. If you preview the Item, you'll see the thumbnail displayed in the list of files you can download.

NOTE: This can be reproduced on https://demo.dspace.org

(I didn't test this for WorkflowItems, but the bug may appear there as well.)

Expected behavior

Since the thumbnail is available, it should be displayed on the MyDSpace page.