WebTorrent: Stats remain stuck after download finishes

[feross]

Description

When a torrent finishes, the stats stop updating and stay stuck on the last state, which may show that e.g. there's still a download rate of 2.4 MB/s (when in fact the download rate is 0 MB/s) as can be seen here:

Steps to Reproduce

1. Visit https://webtorrent.io/free-torrents
2. Click Big Buck Bunny (torrent file)
3. Start torrent download
4. Wait for the download to complete and look at the stats

Actual result:

Stats freeze

Expected result:

Stats continue updating when download is complete

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Version 0.66.101 Chromium: 75.0.3770.142 (Official Build) (64-bit)

Version/Channel Information:

• Can you reproduce this issue with the current release? Yes
• Can you reproduce this issue with the beta channel? Yes
• Can you reproduce this issue with the dev channel? Yes
• Can you reproduce this issue with the nightly channel? Yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? No
• Does the issue resolve itself when disabling Brave Rewards? No
• Is the issue reproducible on the latest version of Chrome? N/A

Miscellaneous Information:

[btlechowski]

Verification passed on

Brave	0.70.96 Chromium: 76.0.3809.132 (Official Build) beta (64-bit)
Revision	fd1acc410994a7a68ac25bc77513d443f3130860-refs/branch-heads/3809@{#1035}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#3004

Verificationn passed on

Brave	0.70.97 Chromium: 77.0.3865.65 (Official Build) beta (64-bit)
Revision	87a331a3169cab563505fb44011058b904011ba1-refs/branch-heads/3865@{#726}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• Verified test plan from WebTorrent: Fix stats remain stuck after download finishes brave-core#3004
  

Verification PASSED on macOS 10.14.6 x64 using the following build:

Brave	0.69.126 Chromium: 77.0.3865.65 (Official Build) (64-bit)
Revision	87a331a3169cab563505fb44011058b904011ba1-refs/branch-heads/3865@{#726}
OS	macOS Version 10.14.6 (Build 18G95)