message: fix RtlGenRandom argument size
diff: @@ -774,7 +774,7 @@ pub trait EvalContextExt<'a, 'mir, 'tcx: 'a + 'mir>: crate::MiriEvalContextExt<'
  // The actual name of 'RtlGenRandom'
  "SystemFunction036" => {
  let ptr = this.read_scalar(args[0])?.to_ptr()?;
  - let len = this.read_scalar(args[1])?.to_usize(this)?;
  + let len = this.read_scalar(args[1])?.to_u32()?;
  if len > 0 {
  let data = gen_random(this, len as usize)?;
  