Fix infinite loop on empty variable name.

test/variables/empty/empty.gypi

Index: test/variables/empty/empty.gypi
diff --git a/test/msvs/rules_stdout_stderr/rule_stdout.py b/test/variables/empty/empty.gypi
similarity index 74%
copy from test/msvs/rules_stdout_stderr/rule_stdout.py
copy to test/variables/empty/empty.gypi
index 2b58d2a374ea5801662d57808ed5b798e6b044a4..e95031fca59b6c18f0e1de74251b4bacffd487e0 100644
--- a/test/msvs/rules_stdout_stderr/rule_stdout.py
+++ b/test/variables/empty/empty.gypi
@@ -1,6 +1,9 @@
-#!/usr/bin/env python
 # Copyright (c) 2015 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-print "This will go to stdout"
+{
+  'variables': {
+    '': '',
+  },
+}