fix files when there are no search results
fix files when there are no search results

fixes ADMIN-1538

test plan:
- have some course files
- enter a search term of at least 3 characters that will not result in
  any hits.
- you should then be able to click on the folders in the file tree to
  navigate.

Change-Id: I797d6d52748c91f17960d6d0240d29f1b1d06a92
Reviewed-on: https://gerrit.instructure.com/169313
Reviewed-by: Carl Kibler <7c2b40129dd885a147d5b2dda56dda016b9a8f57@instructure.com>
QA-Review: Jon Willesen <0321efbc0acf6204eb6035acb1d418838b450d08@instructure.com>
Product-Review: KC Naegle <9fbecd016338f9910821a8a5d5d0ae4fc9abfaa5@instructure.com>
Tested-by: Jon Willesen <0321efbc0acf6204eb6035acb1d418838b450d08@instructure.com>

djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms