panic misusing --json-body argument

Trying to work around a bug in image import, I tried to create an image from a URL. I wasn't sure how to use it:

$ oxide image create
error: the following required arguments were not provided:
  --json-body <JSON-FILE>
  --description <description>
  --name <name>
  --os <os>
  --version <version>

In terms of the json-body, I thought I could guess my way there:

$ echo '{"source": { "url": "http://catacomb.eng.oxide.computer/media/cloud/debian-11-genericcloud-amd64.raw", block_size: 512 } }' | oxide image create --name my-image --description my-description --os debian --version 11 --json-body -
thread 'tokio-runtime-worker' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }', cli/src/generated_cli.rs:5800:59
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: JoinError::Panic(Id(17), ...)', cli/src/main.rs:59:10

I guess it doesn't treat - as stdin and then panicked because it tried to open it and it wasn't there?

Reproduce the command using --json-body - and start at cli/src/generated_cli.rs:5800, then follow the call from cli/src/main.rs:59. Check how the JSON body path is opened and how failures are reported. Done means the command no longer panics when given this input and its stdin or file behavior is handled consistently.