Snap: Perform null check on AF state in updateCaptureStateMachine

 * Some camera HAL implementations don't push AF state to urgent
   metadata. E.g. for QCOM camera HAL this happens only after
https://source.codeaurora.org/quic/la/platform/hardware/qcom/camera/commit/?h=LA.UM.7.2.r1-07700-sdm660.0&id=d276a953295364b967c36038362c1e7ea268bdad
 * Fix crash on capture after c724bc35a9c5f3b36ce36a2081559e2644993da4

Change-Id: I8980fd3fb7d7db4f61189281580ecb17778602df
1 file changed