return a 400 status code for invalid moves

was previously returning 500

services/web/app/coffee/Features/Editor/EditorHttpController.coffee

@@ -128,8 +128,12 @@ module.exports = EditorHttpController =
 		folder_id = req.body.folder_id
 		user_id = AuthenticationController.getLoggedInUserId(req)
 		EditorController.moveEntity project_id, entity_id, folder_id, entity_type, user_id, (error) ->
-			return next(error) if error?
-			res.sendStatus 204
+			if error?.message == 'destination folder is a child folder of me'
+				res.status(400).json(req.i18n.translate('invalid_file_name'))
+			else if error?
+				next(error)
+			else
+				res.sendStatus 204
 
 	deleteDoc: (req, res, next)->
 		req.params.entity_type  = "doc"