The error was not handled, as is the cause for the bug. So far we'd
better wait until a valid image index is ready.

BUG=angleproject:2301

Change-Id: I49a5545d0f2e0cf6cfbb3f604ab0602f8a131d12
Reviewed-on: https://chromium-review.googlesource.com/895402
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>