MusicBrainzClient stop result parsing after reading first medium with correct discid.

Tentative fix for #7020.

src/musicbrainz/musicbrainzclient.cpp

@@ -156,6 +156,7 @@ void MusicBrainzClient::DiscIdRequestFinished(const QString& discid,
             ret << track;
           }
         }
+        break; // stop after consuming one medium with correct discid!
       } else {
         Utilities::ConsumeCurrentElement(&reader);
       }