message: Fix tf.variable_scope unique name after entering root scope
  Closes
diff: @@ -1175,7 +1175,7 @@ class _VariableScopeStore(threading.local):
  def close_variable_subscopes(self, scope_name):
  for k in list(self.variable_scopes_count.keys()):
  - if not scope_name or k.startswith(scope_name + "/"):
  + if scope_name is None or k.startswith(scope_name + "/"):
  self.variable_scopes_count[k] = 0
  def variable_scope_count(self, scope_name):
  