Cannot save cloned Course when using the Classic Editor

### Reproduction Steps

1. Install and Activate the Classic Editor plugin
2. Under Courses, click Clone on a course
3. Go to the Edit screen for the cloned course
4. Attempt to Publish the course

### Expected Behavior

You are able to publish the cloned course

### Actual Behavior

An error appears in the console that elements are not focusable.


The fix is to make the “Number of lessons to make immediately available on course start” and “Delay (in days)” values blank instead of `0` after the course is cloned somehow.

This issue has be recreated:
+ [x] Locally
+ [x] On a staging site
+ [x] On a production website
+ [x] With only LifterLMS and a default theme