Don't override the finished QThread signal in LibraryCreator

This should fix a crash in LibrariesUpdateCoordinator because the QThread can be destroyed before it finishes running.

YACReaderLibrary/library_creator.h

@@ -62,7 +62,7 @@ private:
     void cleanup(QSqlDatabase &db, const QString &target);
 
 signals:
-    void finished();
+    void completed();
     void coverExtracted(QString);
     void folderUpdated(QString);
     void comicAdded(QString, QString);