message: fix copy pasted code
diff: @@ -407,8 +407,8 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  "memrchr" => {
  let ptr = args[0].read_ptr(&self.memory)?;
  - let val = self.value_to_primval(args[1], usize)?.to_u64() as u8;
  - let num = self.value_to_primval(args[2], usize)?.to_u64();
  + let val = self.value_to_primval(args[1], usize)?.to_u64()? as u8;
  + let num = self.value_to_primval(args[2], usize)?.to_u64()?;
  if let Some(idx) = self.memory.read_bytes(ptr, num)?.iter().rev().position(|&c| c == val) {
  let new_ptr = ptr.offset(num - idx as u64 - 1);
  self.write_value(Value::ByVal(PrimVal::Ptr(new_ptr)), dest, dest_ty)?;
  