Fix 'result' variable referenced before assignment issue

This issue is caused by lacking of coverage in code. When we are parsing
json result, value/values doesn't exist in its filed_dict for a key,
this issue will be hitten.

TEST=Eliminated the error caused by this issue.
BUG=chromium:929519

Change-Id: I81e4c0cf5f92c2dca9662ba86629355b3b048089
Reviewed-on: https://chromium-review.googlesource.com/1553681
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Zhizhou Yang <zhizhouy@google.com>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
1 file changed