Fix state sync issue before editor.html is available

[jhebb]

It's possible to miss a model update if the value changes before editor.html is available since Froala's internal state on this.oldModel will be updated with the new value, but not actually displayed visually because editor.html is not available.

I've tried to simulate a basic case here:
https://codesandbox.io/s/froala-react-h7jg6

I'm sure there's a more elegant way to resolve this, but this PR creates a new internal state flag for editor.html availability and triggers setContent even if the props match if the editor was not previously available but is now.

[kapil2704]

@jhebb the link you have shared is not working https://codesandbox.io/s/froala-react-h7jg6 can you please explain the eroor in detail

[jhebb]

The link works for me - it's just showing a number of simulated model updates in succession and showing that the same state value (num) set in a model update and rendered directly get out of sync.