Calling `setState` in `componentWillMount` of a component causes the error

```
TypeError: Cannot read property '_currentElement' of null
    at ReactCompositeComponentMixin._updateRenderedComponent
```

when rendering server-side with `ReactDOMServer.renderToString` and preceded by a component that renders content using `ReactDOMServer.renderToString` or `ReactDOMServer.renderToStaticMarkup`.

Causes TypeError with 0.14.8 and 15.0.0-rc.2:
https://github.com/PKJedi/react-dom-server-test/blob/master/test.js

Works with 0.13:
https://github.com/PKJedi/react-dom-server-test/blob/master/0.13/test.js

/**
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule ReactServerRendering
 */
'use strict';
var ReactDOMContainerInfo = require('ReactDOMContainerInfo');
var ReactDefaultBatchingStrategy = require('ReactDefaultBatchingStrategy');
var ReactElement = require('ReactElement');
var ReactInstrumentation = require('ReactInstrumentation');
var ReactMarkupChecksum = require('ReactMarkupChecksum');
var ReactReconciler = require('ReactReconciler');
var ReactServerBatchingStrategy = require('ReactServerBatchingStrategy');
var ReactServerRenderingTransaction =
  require('ReactServerRenderingTransaction');
var ReactUpdates = require('ReactUpdates');
var emptyObject = require('emptyObject');
var instantiateReactComponent = require('instantiateReactComponent');
var invariant = require('invariant');
/**
 * @param {ReactElement} element
 * @return {string} the HTML markup
 */
function renderToStringImpl(element, makeStaticMarkup) {