Gets the index of the dataset's current page.
The getCurrentPageIndex() function returns the index of current dataset
page. The indices of the dataset's pages start at 1.
Note:
A dataset needs to load its data before you call its getCurrentPageIndex() function.
Usually a dataset finishes loading a short time after the page it is on finishes
loading. So if you call getCurrentPageIndex() inside the page’s onReady()
event handler, the dataset might not be ready yet.
To call getCurrentPageIndex() as soon as possible after a page loads, use the dataset's
onReady() function inside the page’s onReady()
event handler to ensure that both the page and the dataset have finished loading.