Fix: don't cache GraphQL types with no name

[bduncanj]

This addresses issue #1

[jamillosantos]

Hi @bduncanj, I'm very sorry for the delay (totally missed the notification).

Thank you for your contribution. Before merging it I would like to ask you if it is possible to write some tests? The test here would ensure this error will never happen again.

Write a test that documents your problem (a test that breaks without your fix).

Thanks again.

[bduncanj]

Present issue is that the source tests import the lab259 package (go-graphql-struct) and as such don't end up executing the source code in my branch. The other issues I've addressed are:

• Getting Input Object working (use object as argument to mutation)
• Custom GrahpqlTyped (panics because it tries to call Elem() on an interface that isn't a pointer type).

I'll make separate PRs as and when for these other issues.