Fix race condition in render/unmount

[NumminorihSF]

There is a race condition in rendering/unmounting portal.
If you open the portal and unmount parent component, state.active will be false. But portal will be mounted and active. This is because this.setState() may works async. The solution is use the 2nd setState() argument, that is callback.

[Gyran]

I ran into a case where this PR would have saved me.

[dwick]

@tajo this also fixes an issue for me. Any chance this might land soon?

[dwick]

I've forked this and published to https://www.npmjs.com/package/react-portal-fork for those waiting on this to be fixed.

[davidsturgeon]

Ran into this issue as well. Any idea on when a merge into master will happen?

[bradleyayers]

I just ran into it, I think the real fix here should be to use componentDidUpdate rather than componentWillReceiveProps. componentDidUpdate takes into consideration state changes as well as prop changes. I've adapted the code and tested it in my scenario and it seems much more stable.

[tajo]

Hey, please check the new major version (complete rewrite) of react-portal: #157

It's React v16 only since its uses the new official Portal API. There is the first beta released and I would like to get your feedback. I don't have bandwidth to maintain v3 which is very different and full of hacks.

If you feel your PR still applies, please rebase it against the master and re-open it. Sorry for the lack of response in past! Thanks!