message: Fix CodeMemory::new(0)
diff: @@ -137,13 +137,20 @@ impl CodeMemory {
  #[cfg(unix)]
  impl CodeMemory {
  pub fn new(size: usize) -> CodeMemory {
  + if size == 0 {
  + return CodeMemory {
  + ptr: std::ptr::null_mut(),
  + size: 0,
  + };
  + }
  +
  fn round_up_to_page_size(size: usize) -> usize {
  (size + (4096 - 1)) & !(4096 - 1)
  }
  let size = round_up_to_page_size(size);
  let ptr = unsafe {
  mmap(
  - ::std::ptr::null_mut(),
  + std::ptr::null_mut(),
  size,
  PROT_READ | PROT_WRITE,
  MAP_PRIVATE | MAP_ANON,
  