don't recommend things you're already downloading

[ghost]

Please, fill all relevant items:

• I have read CONTRIBUTING.rst

• I have tried with the latest pre-release version and I still can reproduce the issue.

Tribler version/branch+revision:

Installed: 7.0.1-next+2a1d342

Operating system and version:

ubuntu 17.10 artful

Expected behavior:

When tribler recommends torrents to me via the main screen, the 'recommended for you'...I should be able to click on them and download them without hassle.

Actual behavior:

1. I click on one of the torrent's download icon (not saying which one, sorry)
2. the Download Torrent window comes up. click download
3. "Request Error : an error occurred during the request
   this download already exists." ( this error is correct, I am apparently already downloading it )

Steps to reproduce the behavior:

see above

Relevant log file output:

INFO 1521431583.11 server:285 Closing session, reason unspecified
ERROR 1521431583.30 rest_manager:54 [Failure instance: Traceback: <class 'Tribler.Core.exceptions.DuplicateDownloadException'>: <class 'Tribler.Core.exceptions.DuplicateDownloadException'>: This download already exists.
/usr/lib/python2.7/dist-packages/twisted/web/http.py:1442:dataReceived
/usr/lib/python2.7/dist-packages/twisted/web/http.py:1768:_finishRequestBody
/usr/lib/python2.7/dist-packages/twisted/web/http.py:1845:allContentReceived
/usr/lib/python2.7/dist-packages/twisted/web/http.py:766:requestReceived
--- ---
/usr/lib/python2.7/dist-packages/twisted/web/server.py:190:process
/usr/lib/python2.7/dist-packages/twisted/web/server.py:241:render
/usr/lib/python2.7/dist-packages/twisted/web/resource.py:250:render
/usr/share/tribler/Tribler/Core/Modules/restapi/downloads_endpoint.py:295:render_PUT
/usr/share/tribler/Tribler/Core/Session.py:313:start_download_from_uri
/usr/share/tribler/Tribler/Core/Libtorrent/LibtorrentMgr.py:568:start_download_from_uri
/usr/share/tribler/Tribler/Core/Libtorrent/LibtorrentMgr.py:592:start_download_from_magnet
/usr/share/tribler/Tribler/Core/Libtorrent/LibtorrentMgr.py:627:start_download
]
Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/twisted/web/server.py", line 190, in process
self.render(resrc)
File "/usr/lib/python2.7/dist-packages/twisted/web/server.py", line 241, in render
body = resrc.render(self)
File "/usr/lib/python2.7/dist-packages/twisted/web/resource.py", line 250, in render
return m(request)
File "/usr/share/tribler/Tribler/Core/Modules/restapi/downloads_endpoint.py", line 295, in render_PUT
unquote_plus(unicode(parameters['uri'][0], 'utf-8')), download_config)
File "/usr/share/tribler/Tribler/Core/Session.py", line 313, in start_download_from_uri
return self.lm.ltmgr.start_download_from_uri(uri, dconfig=dconfig)
File "/usr/share/tribler/Tribler/Core/Libtorrent/LibtorrentMgr.py", line 568, in start_download_from_uri
return succeed(self.start_download_from_magnet(uri, dconfig=dconfig))
File "/usr/share/tribler/Tribler/Core/Libtorrent/LibtorrentMgr.py", line 592, in start_download_from_magnet
return self.start_download(tdef=tdef, dconfig=dconfig)
File "/usr/share/tribler/Tribler/Core/Libtorrent/LibtorrentMgr.py", line 627, in start_download
raise DuplicateDownloadException("This download already exists.")
DuplicateDownloadException: <class 'Tribler.Core.exceptions.DuplicateDownloadException'>: This download already exists.

Incidentally I think this is part of #21 - if you've got 1000 torrents going, you're going to
a) totally lose track what you are and are not downloading
b) more and more of the 'recommended' stuff, if the recommendation engine is working at all, is going to be a hit if you've got a lot of torrents going.

[xoriole]

@themusicgod1 Thank you for reporting. You are indeed right. We need to improve the recommendation engine.