'iframe' mode editor crashed when destroy before it is not fully initialized

[torrac12]

Though we are using 'react-froala-wysiwyg' library, I believe the issue should be fixed in 'wysiwyg-editor' library

Simplified demo: https://codesandbox.io/s/billowing-paper-pn1fe5?file=/src/App.js.

We found editor crashed in our product if the editor frequently init and destroy, and we simplify the bug to above demo

It only happens in "iframe" mode, seems the editor get destroy before it fully initialized which cause the issue

[dcsaszar]

See also #4342