add logging and defensive code when initializing sensors

sp<SensorEventQueue> SensorManager::createEventQueue()

{

    sp<SensorEventQueue> result = new SensorEventQueue(

            mSensorServer->createSensorEventConnection());

    return result;

    sp<SensorEventQueue> queue;

    if (mSensorServer == NULL) {

        LOGE("createEventQueue: mSensorSever is NULL");

        return queue;

    }

    sp<ISensorEventConnection> connection =

            mSensorServer->createSensorEventConnection();

    if (connection == NULL) {

        LOGE("createEventQueue: connection is NULL");

        return queue;

    }

    queue = new SensorEventQueue(connection);

    return queue;

}

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