cros buildresult: Don't crash if build not found.

If a build doesn't exist in CIDB at all, we need to not crash. We
could be more informative if we queried buildbucket, but not crashing
is a good start.

BUG=chromium:800988
TEST=cros buildresult --buildbucket-id=8956941933144134560

Change-Id: I4d68b7c395fa80c52cbf7a3ac5b491a4db375daf
Reviewed-on: https://chromium-review.googlesource.com/877184
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Jacob Kopczynski <jkop@chromium.org>
1 file changed