better error handling in SensorManager

        res = queue->waitForEvent();

        if (res != NO_ERROR)

            return -1;

        // here we're guaranteed to have an event

        res = queue->read(&event, 1);

        ALOGE_IF(res==0, "sensors_data_poll: nothing to read after waitForEvent()");

    }

    if (res < 0)

    if (res <= 0) {

        return -1;

    }

    jint accuracy = event.vector.status;

    env->SetFloatArrayRegion(values, 0, 3, event.vector.v);