Fix #3009: unable to search for mixed case filenames

[gsnedders]

Fixes #3009.

I'm not sure why the test fails, as far as I can tell from https://polymer-library.polymer-project.org/3.0/docs/devguide/data-system setting queryInput should be running the queryInputChanged observer, which should call latchQuery after half a second, which sets query, which should call the queryUpdated observer, which should set structuredQuery?