Fix Mac OS check for terminal input

runtime/bin/socket_patch.dart

Index: runtime/bin/socket_patch.dart
diff --git a/runtime/bin/socket_patch.dart b/runtime/bin/socket_patch.dart
index 09904b433de13c0144bcca0949fc509ab205b187..1ec51b77795faff13c3a030cd6c553d4ed713ba3 100644
--- a/runtime/bin/socket_patch.dart
+++ b/runtime/bin/socket_patch.dart
@@ -1243,9 +1243,11 @@ class _RawSocket extends Stream<RawSocketEvent>
     native.isClosedWrite = true;
     if (fd != null) _getStdioHandle(native, fd);
     var result = new _RawSocket(native);
-    result._isMacOSTerminalInput =
-        Platform.isMacOS &&
-        _StdIOUtils._socketType(result._socket) == _STDIO_HANDLE_TYPE_TERMINAL;
+    if (fd != null) {
+      var socketType = _StdIOUtils._socketType(result._socket);
+      result._isMacOSTerminalInput =
+          Platform.isMacOS && socketType == _STDIO_HANDLE_TYPE_TERMINAL;
+    }
     return result;
   }