Non-ajax code lacks double submission prevention

Problem/Motivation

I don't quite understand why there needs to be 2 copies of most of the JavaScript for this module, one for non-AJAX and one for AJAX enabled forms, but since there is, there's a little inconsistency between the two.

In particular, the AJAX version has a snippet of code that stops double submission of the actual form, whereas the non-AJAX version does not.

In my testing I was seeing that the browser really was being asked to submit the form twice, but that something was preventing that. Not entirely sure what was, but we could easily bring the fix from the AJAX version into the non-AJAX version.

Steps to reproduce

Look at the code.

Proposed resolution

Copy the code.

Remaining tasks

Prepare and review a MR.

User interface changes

None.

API changes

None.

Data model changes

None.