Rename issues

"make logic more explicit" was an attempt to stop `<model type="xsd:string">`  (Case:65476) happening when there were form errors, due to the fact that the XML isn't actually written until the very end so it seemed like if you had a bad bind element without attrs.nodeset you could end up writing `type="xsd:string"` on the currently open element (model) in the catch-all branch of the conditional here.  This doesn't actually seemed to have fixed that, but it's still a valid change that makes this block of code more semantically correct.

Boo-boo is bad.  ~14 days ago, by forgetting to remove a `false` I appended to a conditional during testing, https://github.com/dimagi/Vellum/pull/68/files#L0R76 I accidentally broke the short-circuiting of node ID / select item value renaming that happens when you clear the value.