Opening external Webtorrent app by magnet causes blank new tab to appear

[Brave-Matt]

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Yes

Description
This was reported in the 'desktop' Discord channel by user Akiba -
When clicking on magnet links, Brave opens a blank new tab in browser when external Webtorrent app

Steps to Reproduce
[Its assumed that you have the external webtorrent app already installed]

1. Ensure "Torrent Viewer" extension is disabled
2. Visit torrent aggregate website
3. Click on magnet link to download/stream torrent in external app

Actual result:
Magnet link launches external app, torrent begins to download/stream, blank new tab appears in browser
https://imgur.com/boev0XV

Expected result:
Magnet link launches external app, torrent begins to download/stream, but should be no blank new tab appears in browser

Reproduces how often:
Frequent enough to notice but hard to tell

about:brave info:
Brave: 0.23.31
V8: 6.7.288.46
rev: 3148ace
Muon: 7.1.5
OS Release: 10.0.17134
Update Channel: Release
OS Architecture: x64
OS Platform: Microsoft Windows
Node.js: 7.9.0
Brave Sync: v1.4.2
libchromiumcontent: 67.0.3396.103

Reproducible on current live release:
Yes

Additional Information
This is clearly low priority but I wanted to submit it anyway. I can also probe for further/different steps to reproduce if necessary