fix(GraphQL) fix empty type Query with single extended type definition in the schema.

[minhaj-shakeel]

Fixes GRAPHQL-1060.

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This change is 

[abhimanyusinghgaur]

Reviewable status: 0 of 3 files reviewed, 1 unresolved discussion (waiting on @minhaj-shakeel and @pawanrawal)

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graphql/schema/gqlschema.go, line 2558 at r1 (raw file):

Quoted 7 lines of code…

	queriesToWrite := false
	for _, fld := range schema.Query.Fields {
		if !strings.HasPrefix(fld.Name, "__") {
			queriesToWrite = true
			break
		}
	}

let's put this logic in a function called hasStringifiableFields(typ *ast.Type) bool and use that