<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
-->

**Do you want to request a *feature* or report a *bug*?**
bug, I believe, unless I misunderstand how it works
**What is the current behavior?**
Given a `Suspense` inside `Suspense` case like
```
<Suspense fallback="Fallback 1">
  <LazyText1 text="First text" />
  <Suspense fallback="Fallback 2">
    <LazyText2 text="Second text!" />
  </Suspense>
</Suspense>
```

Promises in `LazyTexts` start resolving at the same time, but if `LazyText2` is resolved first it never renders, `Fallback 2` stays.

Result:
```
First text

Fallback 2
```

Please see https://codesandbox.io/s/234o4zry7n

**What is the expected behavior?**

Every `LazyText` displayed in the end
```
First text

Second text!
```

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
react, react-dom 16.6.0

'Suspend! [A]',
      'Loading A...',
      'Suspend! [B]',
      'Loading B...',
    ]);
    expect(root).toMatchRenderedOutput(null);
    
    jest.advanceTimersByTime(4000);
    expect(root).toFlushWithoutYielding();
    expect(root).toMatchRenderedOutput('Loading A...Loading B...');
    
    
    
    jest.advanceTimersByTime(1000);
    
    expect(ReactTestRenderer).toHaveYielded(['Promise resolved [A]']);
    expect(root).toFlushAndYield(['A']);
    expect(root).toMatchRenderedOutput('ALoading B...');
    
    
    jest.advanceTimersByTime(1000);
    expect(ReactTestRenderer).toHaveYielded(['Promise resolved [B]']);
    expect(root).toFlushAndYield(['B']);
    expect(root).toMatchRenderedOutput('AB');
  });
  it('interrupts current render if promise resolves before current render phase', () => {
    let didResolve = false;
    let listeners = [];
    const thenable = {
      then(resolve) {