Don't report hasTerminal, if term-size is (0,0).

runtime/bin/stdio_macos.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include <errno.h>  // NOLINT
 #include <sys/ioctl.h>  // NOLINT
 #include <termios.h>  // NOLINT
@@ skipping 49 matching lines @@
   } else {
     term.c_lflag &= ~(ICANON);
   }
   tcsetattr(STDIN_FILENO, TCSANOW, &term);
 }
 
 
 bool Stdout::GetTerminalSize(int size[2]) {
   struct winsize w;
   if (TEMP_FAILURE_RETRY_BLOCK_SIGNALS(
-        ioctl(STDOUT_FILENO, TIOCGWINSZ, &w) != 0)) {
-    return false;
+        ioctl(STDOUT_FILENO, TIOCGWINSZ, &w) == 0) &&
+      (w.ws_col != 0 || w.ws_row != 0)) {
+    size[0] = w.ws_col;
+    size[1] = w.ws_row;
+    return true;
   }
-  size[0] = w.ws_col;
-  size[1] = w.ws_row;
-  return true;
+  return false;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)