Fixes leak of native File objects.

runtime/bin/file_macos.cc

Index: runtime/bin/file_macos.cc
diff --git a/runtime/bin/file_macos.cc b/runtime/bin/file_macos.cc
index 81412f66e0c4440a4898e8bf8076cfae33fe7fcd..c6de3212daf285cf03be64ea0e08f5a85d8bbca7 100644
--- a/runtime/bin/file_macos.cc
+++ b/runtime/bin/file_macos.cc
@@ -40,7 +40,9 @@ class FileHandle {
 
 
 File::~File() {
-  Close();
+  if (!IsClosed()) {
+    Close();
+  }
   delete handle_;
 }
 
@@ -199,10 +201,7 @@ File* File::Open(const char* path, FileOpenMode mode) {
 
 
 File* File::OpenStdio(int fd) {
-  if ((fd < 0) || (2 < fd)) {
-    return NULL;
-  }
-  return new File(new FileHandle(fd));
+  return ((fd < 0) || (2 < fd)) ? NULL : new File(new FileHandle(fd));
 }