Fix Exceptions Thrown During ScrollList Init With No Items

Unit Tests
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- Cover scenario where bug is thrown by ScaleTranslator

How To +10/QA
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`./init.sh && grunt qa`

- Should see no console errors.
- Update example app so that enpty array is returned here: https://github.com/WebFilings/wf-uicomponents/blob/master/examples/scroll_list/scroll-list.js#L51
- View ScrollList demo
- Should see no items rendered and no console errors.

@patkujawa-wf 
@robbecker-wf 
@lancefisher-wf