Dashboard - Fix exception in test-picker
Dashboard - Fix exception in test-picker

This always failed in the past, and was caught via the catch(e). Since
this actually succeeded, we hit an undefined diagnostics exception
since it's defined in the try block.

Bug: catapult:#4237
Change-Id: Ib53234822b56451e849593a01d562e04e49bb553
Reviewed-on: https://chromium-review.googlesource.com/907529
Reviewed-by: Ethan Kuefner <b3258c73b307e35b2725bc68d7434c38b3a2b146@chromium.org>
Commit-Queue: Simon Hatch <490a224d89645d3fea983d7189ce51bde0a00c1d@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult