Add Guard for invalid readyState in IE9 and IE10

IE9 and IE10 can get into a state where 

```javascript
document.readyState === "interactive" // => true
```

even though the document is not yet ready. This happens when a script tag is added dynamically to A dom (can be detached fragment). Looked for tests but only saw the html file. Need to find solid way to repro this case.