Fix PDP images not associated with variant/options

[desaawa]

This fixes #2647

Steps to test

1. As admin, select a variant option in PDP
2. Click on the thumbnails to upload image for the variant.

1. Observe that the image is attached to the selected variant. And if you select another option, you should not see the image

[aaronjudd]

This resolved the upload behavior for variants. It appears the broken "variant" layout in the product grid is a separate issue (and still broken).

[aaronjudd]

@zenweasel since you disagreed (in theory) with this behaviour, can you take a look and see if it makes sense or not to you?

[brent-hoover]

Yeah, I think it makes sense once you realize you have to select the top-level variant to be able to modify the "product" image and that just "deselecting" the options does not allow you to set the top-level images.