Fix falling in dev mode

[Yeti-or]

FiberNode.stateNode could be null

So I get TypeError:

  at performWorkOnRoot (/tmp/my-project/node_modules/react-dom/cjs/react-dom.development.js:11014:24) TypeError: Cannot read property '_warnedAboutRefsInRender' of null
          at findDOMNode (/tmp/my-project/node_modules/react-dom/cjs/react-dom.development.js:15264:55)

I checked react-native-render render in dev it has the same check:
https://github.com/facebook/react/blob/master/packages/react-native-renderer/src/findNodeHandle.js#L73

react/packages/react-native-renderer/src/findNodeHandle.js

Line 73 in 6031bea

if (owner !== null && owner.stateNode !== null) {

[gaearon]

I think this is reasonable but can we get a reproducing case as a test so we don't regress again?
I'd like to better understand why #12299 is happening.

[Yeti-or]

@gaearon okay I'll try

[raunofreiberg]

@gaearon https://codesandbox.io/s/4jmz84q147

Might not be what you're quite looking for but I've seen this happen in a similar manner before.

[gaearon]

OK, I think this is fine to get in but I'd appreciate a follow-up PR with a test so we don't regress.