Header overlay control should be conditionally visible

[timelsass]

Describe the bug
Header overlay control is visible when there is no video or image set to be displayed on the background. The control only changes the overlay on the header.

To Reproduce
Steps to reproduce the behavior:

1. Go to WP Customizer
2. Click on Design section
3. Click on Header section
4. Click on Background Section
5. Make sure you don't have a background image or video set.
6. Scroll down to bottom.

The result is that the header overlay control is visible.

Expected behavior
The header overlay control should only be visible when there is a background image or video present.

Screenshots