Do not patch function if already patched, support reexporting page and getServerSideProps

[remorses]

Currently if you reexport a page and gssp function you will get an error, because the props are serialized 2 times

This is an example page with the problem:

import Page from './page'
import { getServerSideProps } from './page'

export default Page
export { getServerSideProps }

[serg-and]

Hi, this plugin seems to no longer be maintained. Feel free to add your PR in this fork https://github.com/serg-and/superjson-next