Fix null pointer WifiInfo

The WifiInfo cached in ActiveModeWarden should never be null. Currently
it's null until a ClientModeImpl starts, which may not happen in a while
if wifi is off at bootup.

Bug: 286470772
Test: atest com.android.server.wifi
Change-Id: I7b9ed213c4582861f86a5614fd5091200b382267
1 file changed