schema: Resolve: only dereference schema when needed

Since we may not need the schema at all to resolve the path (and now we
may not even have it), let's not dereference it until necessary.

Author: Antoine Pelisse

schema/elements.go

@@ -207,7 +207,7 @@ func (s Schema) FindNamedType(name string) (TypeDef, bool) {
 //
 // This allows callers to not care about the difference between a (possibly
 // inlined) reference and a definition.
-func (s Schema) Resolve(tr TypeRef) (Atom, bool) {
+func (s *Schema) Resolve(tr TypeRef) (Atom, bool) {
 	if tr.NamedType != nil {
 		t, ok := s.FindNamedType(*tr.NamedType)
 		if !ok {