handle going to go a folder that doesn't exist elegantly

fixes: CNVS-16050

test plan:
go to
/courses/x/files/folder/a/folder/that/does/not/exist

it should look like: http://cl.ly/image/2e1S1H2l3f0I

Change-Id: I5aa130689ff292b42ffef945b7911168f5dc9bc9
Reviewed-on: https://gerrit.instructure.com/42256
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Dan Minkevitch <dan@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>