ref(nextjs): Don't assert existance of pageProps in _app

[lforst]

Even though the Next.js docs tell users to call App.getInitialProps(appContext) in their custom _app pages, many of them don't and this will crash our implementation because the user's getInitialProps will most likely not contain a pageProps property.

This PR adds a simple check if the pageProps are there, and inserts them if they aren't. This should not have any negative consequences.

[AbhiPrasad]

m: can we test this?

[lforst]

m: can we test this?

It would require us to have an intentionally faulty (more or less global) configuration in our Next.js integration tests. Wdyt?

[Lms24]

+1 on a quick test if possible. Otherwise LGTM

EDIT: Just saw your comment. If you think this is too much hassle, I'm fine with not testing the edge case (logaf low)

[AbhiPrasad]

It would require us to have an intentionally faulty (more or less global) configuration in our Next.js integration tests.

hmm yeah that’s right, there’s only 1 app set up. Can we somehow edit the app for just a single test? Like send a header via the request sent. Otherwise is it possible we unit test this somehow for regression test purposes?

if it’s too hard np, we can just ship