[Feature] Filter Markers tab by "Is missing thumbnail/preview"

[UncertainMongoose]

Is your feature request related to a problem? Please describe. I like the (relatively) new feature of sorting tags, scenes, performers, etc. by "Is missing image" for example.

Describe the solution you'd like I'd like to be able to do the same with markers so that I can filter by which markers are missing previews.

Describe alternatives you've considered The only option I've been able to find is filtering by created date since usually the most recently created don't have thumbnails or previews but it could be helpful to have a bit more control over it.