message: Avoid using `as` cast
diff: @@ -174,19 +174,19 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  let buf = this.read_scalar(buf_op)?.not_undef()?;
  if let Some(handle) = this.machine.file_handler.handles.get_mut(&fd) {
  + let count = helpers::try_into_host_usize(count)
  + .ok_or_else(|| err_unsup_format!("Program tries to read into buffer too big for this host platform"))?;
  // We want to read at most `count` bytes
  - let mut bytes = vec![0; count as usize];
  + let mut bytes = vec![0; count];
  let result = handle.file.read(&mut bytes);
  match result {
  Ok(c) => {
  - if let Some(read_bytes) = helpers::try_from_host_usize::<i64>(c) {
  + let read_bytes = helpers::try_from_host_usize::<i64>(c)
  + .ok_or_else(|| err_unsup_format!("Number of read bytes {} cannot be transformed to i64", c))?;
  // If reading to `bytes` did not fail, we write those bytes to the buffer.
  this.memory.write_bytes(buf, bytes)?;
  Ok(read_bytes)
  - } else {
  - throw_unsup_format!("Number of read bytes {} cannot be transformed to i64", c);
  - }
  },
  Err(e) => {
  this.set_last_error_from_io_error(e)?;
  @@ -221,13 +221,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  let result = handle.file.write(&bytes);
  match result {
  - Ok(c) => {
  - if let Some(written_bytes) = helpers::try_from_host_usize::<i64>(c) {
  - Ok(written_bytes)
  - } else {
  - throw_unsup_format!("Number of written bytes {} cannot be transformed to i64", c);
  - }
  - },
  + Ok(c) => helpers::try_from_host_usize::<i64>(c)
  + .ok_or_else(|| err_unsup_format!("Number of written bytes {} cannot be transformed to i64", c).into()),
  Err(e) => {
  this.set_last_error_from_io_error(e)?;
  Ok(-1)
  