Fix 'Replace File' dialog

The REPLACE button in the Replace File dialog opened when click on the Replace blob action should not be clickable as long as the file is uploading.

How to reproduce:

• navigate to a Picture document
• click on the Replace blob action under the image preview
• (throttle the network speed in the browser dev tools to a very slow speed)
• click on the Upload main file link in the Replace File dialog and select a large image

Expected result: the REPLACE button is disabled until the file is uploaded
Actual result: the REPLACE button is immediately active even if the file is not completely uploaded