Clean-up Context#stack.

lib/liquid/context.rb

@@ -86,17 +86,11 @@ module Liquid
     #   end
     #
     #   context['var]  #=> nil
-    def stack(new_scope={},&block)
+    def stack(new_scope={})
-      result = nil
       push(new_scope)
-
+      yield
-      begin
+    ensure
-        result = yield
+      pop
-      ensure
-        pop
-      end
-
-      result
     end
 
     def clear_instance_assigns