As reported in #313 and #384, an error thrown that isn't a
`HttpQueryError` will result in an "unhandled promise rejection",
leading to infinitely hanging requests.
While exploring ways to reproduce #313, I thought that validation errors
coming from GraphQL's internal type checking would reproduce the issue.
It didn't. But instead of throwing out the test I wrote, I thought it
might be good to keep it around to prevent future possible regressions.
I'll keep exploring ways to reproduce the issue I'm experiencing in a
subsequent commit(s).