Autofill Fix Latency Metrics

Fix unexpected cases where
t.metric_array.metric.event.autofill.event_autofill_fill_response_reported.atom.latency_response_processing_millis is not initialized

Test: locally test metric is logged
Fixes: 326516791
Change-Id: Id973cb4d9ee7d181276585e86fda830ec3ce42a6