Fixed getOffsetIndex() and getRowOffset() not using their exposed API methods

`getOffsetIndex()` and `getRowOffset()` were being called internally by their private function symbols - this PR changes the internal calls to target the exposed API method symbols instead.

This is needed in order to allow plugins to successfully override these methods. I figured that this is a good change to make because these functions are *already* explicitly exposed as part of the API, so I considered it an oversight that the exposed methods weren't being used internally as well.