Fix Publish button incorrectly enabled in nuxeo-internal-publish

When selecting 2+ documents and attempting to Publish them via the RESULTS_SELECTION_ACTIONS slot, the "PUBLISH" button in the nuxeo-internal-publish layout is enabled while the Location field is empty. Clicking the button in this state emits an error in the console.

Steps to Reproduce:

1. In a results view (e.g. Folderish, Asset Search), Select 1+ Documents.
2. Click the "Publish" action from the top toolbar
3. Observe the displayed nuxeo-dialog

Expected result: the "PUBLISH" button is disabled until a Location is specified.

Actual result: the "PUBLISH" button is enabled. Clicking this button emits an uncaught TypeError in the browser console.

(see attached pictures for reference)