Describe the bug
The initial frame in the images example results in a size_hint of [4984.0, 0.0] passed to the ferris SVG. Prior to #3719 an invalid size hint for a SVG would error out while creating the pixmap, but now it runs into an unwrap on creating an IntSize, triggering a panic.

To Reproduce
Steps to reproduce the behavior:

1. Checkout 0.25.0 or 963be24
2. Add cc.egui_ctx.set_pixels_per_point(2.0); to the app creator in examples/images/src/main.rs
3. Run the example with cargo run -p images
4. Get thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', crates\egui_extras\src\image.rs:248:83 at IntSize::from_wh(w, h).unwrap() because h is 0 from available_size

Expected behavior
There is no panic

Desktop (please complete the following information):

• OS: Windows
• Version 0.25.0