Fix image_loader for animated image types

[BSteffaniak]

Hi, after upgrading to 0.31.0 all of my beautiful static webp images started failing to load. I use the image_loader to load those via the image crate.

I noticed that with 0.31.0 there are additions to how animated image types are handled with frames and such. And with those changes the frame index is attached to the uri at the end. This was problematic for the image_loader, because it wasn't updated to handle that frame tag at the end of the uri, so when looking up the bytes, it would fail to match the uri in the bytes cache (the bytes were being saved without the frame index, but attempting to be fetched with the frame index).

This fixes the image_loader for me with webp & gif. They don't load the animations, but I think that is because I don't have the custom image_loader set up so I'm not worried about that for myself. I'm not sure if that part is problematic in general, or if its just the way I have my features set up.

You can recreate the issue on master by swapping out the dependency features in the images example like this:

# egui_extras = { workspace = true, features = ["default", "all_loaders"] }
# env_logger = { version = "0.10", default-features = false, features = [
#   "auto-color",
#   "humantime",
# ] }
# image = { workspace = true, features = ["jpeg", "png"] }
egui_extras = { workspace = true, features = ["image", "svg"] }
env_logger = { version = "0.10", default-features = false, features = [
  "auto-color",
  "humantime",
] }
image = { workspace = true, features = ["jpeg", "png", "webp", "gif"] }

• I have followed the instructions in the PR template

[BSteffaniak]

Side note: I think an even better way to handle this would be to not treat static webp/gif images as "animated". The webp spec has an "ANIM" chunk at a specific position in the headers if it is animated, which you could use to determine in addition to searching for the RIFF WEBP header.

I'd be happy to help out with that if you'd like. Otherwise I thought I'd just bring it to your attention in case you haven't thought about that.

[BSteffaniak]

@emilk Do you have any concerns with this approach? Without this, my images don't work with the custom image_loader.