sync op result serialization errors result in panic and abort

[tim-palmer]

If an error occurs in serde_v8 when converting the output of a sync op, it results in a panic and the process aborts.

The panic occurs because unwrap() is called on the result from serde_v8::to_v8. (The resulting panic then causes the whole process to abort, maybe due to denoland/rusty_v8#534.)

Example - this test results in "fatal runtime error: failed to initiate panic, error 5":

#[test]
fn test_serde_v8_error() {
  use serde::ser::{Serialize, Serializer};

  struct ErrOnSerialize;

  impl Serialize for ErrOnSerialize {
    fn serialize<S>(&self, _serializer: S) -> std::result::Result<S::Ok, S::Error> where S: Serializer {
      Err(serde::ser::Error::custom("always errors"))
    }
  }

  #[op]
  fn op_err() -> Result<ErrOnSerialize, anyhow::Error> {
    Ok(ErrOnSerialize)
  }

  run_in_task(|cx| {
    let ext = Extension::builder().ops(vec![op_err::decl()]).build();
    let mut runtime = JsRuntime::new(RuntimeOptions {
      extensions: vec![ext],
      ..Default::default()
    });
    runtime
      .execute_script(
        "test_serde_v8_error.js",
        "Deno.core.opSync('op_err')",
      )
      .unwrap();
    if let Poll::Ready(Err(_)) = runtime.poll_event_loop(cx, false) {
      unreachable!();
    }
  });
}