message: Fix the pointer comparison in windows subprocess.
diff: @@ -134,7 +134,7 @@ void SubProcess::FreeArgs() {
  void SubProcess::ClosePipes() {
  for (int i = 0; i < kNFds; i++) {
  - if (parent_pipe_[i] >= 0) {
  + if (parent_pipe_[i] != nullptr) {
  CloseHandle(parent_pipe_[i]);
  parent_pipe_[i] = nullptr;
  }
  @@ -272,7 +272,7 @@ bool SubProcess::Start() {
  if (bSuccess) {
  for (int i = 0; i < kNFds; i++) {
  - if (child_pipe_[i] >= 0) {
  + if (child_pipe_[i] != nullptr) {
  CloseHandle(child_pipe_[i]);
  child_pipe_[i] = nullptr;
  }
  