Swap the order of setting the preprocessState

As described in https://github.com/23/resumable.js/issues/114#issuecomment-33264668:

I think the problem is here:

https://github.com/23/resumable.js/blob/master/resumable.js#L456

The `$.preprocessState` needs to be set to `1` _before_ calling `preprocess($)`. Otherwise, the `$.preprocessState` gets reset to `1` after the preprocessing occurs, even after calling `.preprocessFinished()`