视频下载合并出错

[MC-dusk]

D:\quickuse\BBDown>BBDown -tv -ia -mt av839127377
BBDown version 1.3.6, Bilibili Downloader.
欢迎到讨论区交流：
https://github.com/nilaoda/BBDown/discussions
[2020-12-13 17:13:24.337] - 加载本地token...
[2020-12-13 17:13:24.337] - 获取aid...
[2020-12-13 17:13:24.338] - 获取aid结束: 839127377
[2020-12-13 17:13:24.339] - 获取视频信息...
[2020-12-13 17:13:24.495] - 视频标题: 一个视频说清整个英语语法体系(重塑你的语法认知框架)
[2020-12-13 17:13:24.495] - 发布时间: 20/08/06 19:38:08
[2020-12-13 17:13:24.496] - P1: [221212485] [yufatixi] [27m07s]
[2020-12-13 17:13:24.498] - 共计 1 个分P, 已选择：ALL
[2020-12-13 17:13:24.498] - 开始解析P1...
[2020-12-13 17:13:24.623] - 共计8条视频流.
0. [1080P 高清] [AVC] [295 kbps] [~58.59 MB]
1. [1080P 高清] [HEVC] [281 kbps] [~55.81 MB]
2. [720P 高清] [AVC] [209 kbps] [~41.51 MB]
3. [720P 高清] [HEVC] [200 kbps] [~39.72 MB]
4. [480P 清晰] [HEVC] [157 kbps] [~31.18 MB]
5. [480P 清晰] [AVC] [155 kbps] [~30.78 MB]
6. [360P 流畅] [HEVC] [158 kbps] [~31.38 MB]
7. [360P 流畅] [AVC] [108 kbps] [~21.45 MB]
[2020-12-13 17:13:24.631] - 共计3条音频流.
0. [M4A] [191 kbps] [~37.93 MB]
1. [M4A] [132 kbps] [~26.22 MB]
2. [M4A] [67 kbps] [~13.31 MB]
[2020-12-13 17:13:24.636] - 请选择一条视频流(输入序号): 7
[2020-12-13 17:13:31.417] - 请选择一条音频流(输入序号): 2
[2020-12-13 17:13:32.065] - 已选择的流:
[视频] [360P 流畅] [AVC] [108 kbps] [~21.44 MB]
[音频] [M4A] [67 kbps] [~13.30 MB]
[2020-12-13 17:13:32.068] - 开始多线程下载P1视频...
[2020-12-13 17:13:34.207] - 合并视频分片...
[2020-12-13 17:13:34.221] - 清理分片...
Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index

经测试，若视频流选480p以上（不含），正常；否则合并时报错

经测试，去掉-mt多线程下载命令，正常

老版本v1.2无此问题（使用“BBDown -tv -ia -mt av839127377”下载合并正常）