Rearrange nested schema expansion

This is simply to make it easier to see the change in the next commit,
which addresses an edge case in the nested expansion.

lib/json_schema/reference_expander.rb

@@ -110,21 +110,23 @@ def dereference(ref_schema, ref_stack)
       # references.
       if ref.uri
         schema_children(new_schema) do |subschema|
-          next if subschema.expanded?
-          next unless subschema.reference
-
           # Don't bother if the subschema points to the same
           # schema as the reference schema.
           next if ref_schema == subschema
 
-          if !subschema.reference.uri
-            # the subschema's ref is local to the file that the
-            # subschema is in; however since there's no URI
-            # the 'resolve_pointer' method would try to look it up
-            # within @schema. So: manually reconstruct the reference to
-            # use the URI of the parent ref.
-            subschema.reference = JsonReference::Reference.new("#{ref.uri}#{subschema.reference.pointer}")
+          next if subschema.expanded?
+
+          if subschema.reference
+            if !subschema.reference.uri
+              # the subschema's ref is local to the file that the
+              # subschema is in; however since there's no URI
+              # the 'resolve_pointer' method would try to look it up
+              # within @schema. So: manually reconstruct the reference to
+              # use the URI of the parent ref.
+              subschema.reference = JsonReference::Reference.new("#{ref.uri}#{subschema.reference.pointer}")
+            end
           end
+
           dereference(subschema, ref_stack)
         end
       end