fix: [torrust#230] make sure user exist in upload torrent endpoint

We get the user ID from the Json Web Token, but that does not mean the user actually exists. The session could be valid, but the user could have been removed from the database.

src/services/torrent.rs

@@ -99,6 +99,8 @@ impl Index {
     /// * Unable to insert the torrent into the database.
     /// * Unable to add the torrent to the whitelist.
     pub async fn add_torrent(&self, mut torrent_request: AddTorrentRequest, user_id: UserId) -> Result<TorrentId, ServiceError> {
+        let _user = self.user_repository.get_compact(&user_id).await?;
+
         torrent_request.torrent.set_announce_urls(&self.configuration).await;
 
         let category = self