Fix get_result_summaries() to never return None items.
Fix get_result_summaries() to never return None items.

This may happen when a TaskRequest without its corresponding TaskResultSummary
was created.

TBR=vadimsh@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1415403002

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py