Fix initial collection of WifiActivityEnergyInfo

We should not assume that the initial WifiActivityEnergyInfo
would be empty. The data in that object comes from the
WiFi controller, which may have accumulated stats since
the hardware reset.

Bug: 351648321
Test: atest PowerStatsTests; atest PowerStatsTestsRavenwood
Flag: com.android.server.power.optimization.streamlined_connectivity_battery_stats


Change-Id: If6168457aa72874d61145bc8c39640488f11dfd3