WebTorrent.remove method removes correct torrent and, incorrectly, the last torrent

[LostBeard]

What version of this package are you using?
2.2.0

What operating system, Node.js, and npm version?
Browser, Chrome 64bit, Windows 10

What happened?
(client is WebTorrent instance)
Calling client.remove(torrent.infoHash) with a valid torrent will remove that torrent but also remove the last torrent in client.torrents also.

The reason is:
client.remove() calls client_remove() where the below line is used without checking if the this.torrents.indexOf(torrent) returns -1, which would be fine if client._remove() was not called again by torrent._destroy() when it (_remove) calls torrent.destroy().

webtorrent/index.js

Line 414 in ff83504

this.torrents.splice(this.torrents.indexOf(torrent), 1)

The code that causes allows the issue:

index.js (WebTorrent)

webtorrent/index.js

Lines 402 to 419 in ff83504

	async remove (torrentId, opts, cb) {
	if (typeof opts === 'function') return this.remove(torrentId, null, opts)
	this._debug('remove')
	const torrent = await this.get(torrentId)
	if (!torrent) throw new Error(`No torrent with id ${torrentId}`)
	this._remove(torrent, opts, cb)
	}
	_remove (torrent, opts, cb) {
	if (!torrent) return
	if (typeof opts === 'function') return this._remove(torrent, null, opts)
	this.torrents.splice(this.torrents.indexOf(torrent), 1)
	torrent.destroy(opts, cb)
	if (this.dht) {
	this.dht._tables.remove(torrent.infoHash)
	}
	}

torrent.js

webtorrent/lib/torrent.js

Lines 748 to 760 in ff83504

	destroy (opts, cb) {
	if (typeof opts === 'function') return this.destroy(null, opts)
	this._destroy(null, opts, cb)
	}
	_destroy (err, opts, cb) {
	if (typeof opts === 'function') return this._destroy(err, null, opts)
	if (this.destroyed) return
	this.destroyed = true
	this._debug('destroy')
	this.client._remove(this)

What did you expect to happen?
I expected only 1 torrent to be removed.

Are you willing to submit a pull request to fix this bug?
Yes. I have a pull request ready.

[LostBeard]

To reproduce the bug

The below code can be pasted into a website console to test for the bug. The example uses the jsdelivr site to load the webtorrent.min.js in this GitHub repo's dist folder.

The magnet links are Big Buck Bunny and Sintel from the free magnet links page.

Steps to reproduce:

var WebTorrentModule = await import('https://cdn.jsdelivr.net/gh/webtorrent/webtorrent/dist/webtorrent.min.js');
var WebTorrent = WebTorrentModule.default;
console.log('WebTorrent.VERSION', WebTorrent.VERSION);
// prints "WebTorrent.VERSION 2.2.0"
var client = new WebTorrent();
// Sintel and Big Buck Bunny magnets (trimmed to just hashes for brevity)
var magnets = [ 'magnet:?xt=urn:btih:08ada5a7a6183aae1e09d831df6748d566095a10', 'magnet:?xt=urn:btih:dd8255ecdc7ca55fb0bbf81323d87062db1f6d1c' ];
client.add(magnets[0]);
client.add(magnets[1]);
console.log('torrents.length', client.torrents.length);
// prints "torrents.length 2"
// calling the below line will cause both the specified torrent and then the last torrent in client.torrents to be removed
await client.remove(magnets[0]);
console.log('torrents.length', client.torrents.length);
// prints "torrents.length 0" due to bug
// should print "torrents.length 1"

(Edited to simplify example code)