fix: files not rendered or contents not substituted when previous list empty

**Description** Rendering fails if you have two or more list variables and a previous list is empty. **Steps To Reproduce** 1. Create a brick that uses loops. See [example](https://github.com/felangel/mason/blob/9aa0213d8761f3954154e6ee7b498151095f4787/packages/mason/test/bricks/loop/__brick__/main_%7B%7B%23values%7D%7D%7B%7B%7B.%7D%7D%7D%7B%7B/values%7D%7D.txt) 2. Generate the brick with parameters that include an empty list preceding the list with information to be rendered ```dart { 'emptyList': <String>[], 'values': ['development', 'staging', 'production'], } ``` 3. Files are either not rendered or the contents are not substituted **Expected Behavior** List with information should be rendered