am 4b2932fb: Fix a crash for a race condition during Bluetooth shutdown

    p_buf->event = BTIF_MEDIA_STOP_AA_TX;

    /*

     * Explicitly check whether the btif_media_cmd_msg_queue is not NULL to

     * avoid a race condition during shutdown of the Bluetooth stack.

     * This race condition is triggered when A2DP audio is streaming on

     * shutdown:

     * "btif_a2dp_on_stopped() -> btif_media_task_stop_aa_req()" is called

     * to stop the particular audio stream, and this happens right after

     * the "cleanup() -> btif_a2dp_stop_media_task()" processing during

     * the shutdown of the Bluetooth stack.

     */

    if (btif_media_cmd_msg_queue != NULL)

        fixed_queue_enqueue(btif_media_cmd_msg_queue, p_buf);

    return TRUE;

}

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