Fix undefined default_config_path_bak in gsutil config.

third_party/gsutil/gslib/commands/config.py

Index: third_party/gsutil/gslib/commands/config.py
diff --git a/third_party/gsutil/gslib/commands/config.py b/third_party/gsutil/gslib/commands/config.py
index edef87f904d0b15aab6eae392dba9ef1277c8d23..5857764f42390f97ad5e433ba960060962d42660 100644
--- a/third_party/gsutil/gslib/commands/config.py
+++ b/third_party/gsutil/gslib/commands/config.py
@@ -594,6 +594,7 @@ class ConfigCommand(Command):
     if not scopes:
       scopes.append(SCOPE_FULL_CONTROL)
 
+    default_config_path_bak = None
     if output_file_name is None:
       # Check to see if a default config file name is requested via
       # environment variable. If so, use it, otherwise use the hard-coded
@@ -607,7 +608,6 @@ class ConfigCommand(Command):
         default_config_path = os.path.expanduser(os.path.join('~', '.boto'))
       if not os.path.exists(default_config_path):
         output_file_name = default_config_path
-        default_config_path_bak = None
       else:
         default_config_path_bak = default_config_path + '.bak'
         if os.path.exists(default_config_path_bak):