Don't build non-existent image URLs

[chickdan]

I believe this fixes #884 as an image URL will only be returned if there are image tags, and without a URL LazyImage should result in the failure case. I don't have a Jellyfin server setup so I could be wrong with my changes so guidance would be appreciated.

[LePips]

So currently, that fix would actually break backdrop images, my bad. I took a look again at these fields because I forgot they're split, imageTags and backdropImageTags to say a few. Backdrop image tags aren't in imageTags, so this will always fail for them. We will have to switch on the type of image being requested and retrieve + check in the right place. In the case for backdrops, we will always take the first (primary) image. This has always worked before because calling for an item backdrop image without an index/tag will just return the primary image.

[chickdan]

We will have to switch on the type of image being requested and retrieve + check in the right place.

Added a new function that switches on ImageType, most of the types do not have corresponding <>ImageTag fields so it defaults to imageTags as that's also how the behavior was previously.

Backdrop image tags aren't in imageTags, so this will always fail for them... In the case for backdrops, we will always take the first (primary) image.

For this, I return backdropImageTags.first from the new getImageTag() function.

This has always worked before because calling for an item backdrop image without an index/tag will just return the primary image.

Considering the existing function always worked with a nil tag as long as the type was .backdrop I added a check to allow the request to be made.

Hopefully, I understood the requirements 🙂 let me know if further adjustments are required.