Allow existing classes to be present

Problem/Motivation

When adding a media item in ckeditor, the filter is not applied because the wrapper already contains a class.

Steps to reproduce

Create a ckeditor config where you can add images (direct upload) and media items.
Create a page with a ckeditor block/content with a direct upload image and a media image.
Observe the image only being photoswiped for the direct upload.

Proposed resolution

Update IF logic.

Remaining tasks

MR

User interface changes

N/A

API changes

N/A

Data model changes