Fix image centering in nuxeo-image-viewer

When viewing a Picture document, the image found within the nuxeo-image-viewer element does not automatically center.

Steps To Reproduce:

1. Navigate to a Picture document in Web UI
2. Remove main file.
3. Upload a new picture file and reload page.

Expected result: the image preview center aligns relative to nuxeo-picture-view-layout

Actual result: the image aligns right side and when close the sidebar after the image preview loads using the  button then image stretches to the full layout.

(see attached screenshot for reference)