Able up select and upload a media item at the same time for a field limited to one item(s)

Problem/Motivation

Bit of an edge case this one, but users are able to add more than one media item to a field that has been limited to just one item. When saving they then see a 'Image: this field cannot hold more than 1 values.' message.

This does stop them saving the node, but it would be great if the user could be blocked before this.

Steps to reproduce

• Setup a media reference field on a node and limit to one value allowed
• Make sure you have at least one item in the media library already
• Add a new node and click 'Add media' on the field
• Select an existing media item (other items are then greyed out)

• Then click on the 'Browse' button on the add media section of the media library
• Upload another file
• You will then go back to the media library with both media items selected

• Click 'Insert selected'

• Click save on the form
• See the 'Image: this field cannot hold more than 1 values.' error

Proposed resolution

If possible I think it would be best to disable the 'Browse' button when the media item has been selected. In this case its a single item, but in the case of multiples it should grey out when the field limit is hit.

This is VERY much an edge case, but possible for a content editor with no much Drupal experience to bump into.

Cheers

Tom