Make ComicQueryResultProcessor::modelData() static

The function doesn't use data members or other member functions. It
could even be put into an unnamed namespace in the cpp file, but that
would require more changes and complicate turning it back into a member
function if need be in the future.

YACReaderLibrary/db/comic_query_result_processor.h

@@ -25,7 +25,7 @@ signals:
 private:
     ConcurrentQueue querySearchQueue;
 
-    QList<ComicItem *> *modelData(QSqlQuery &sqlquery);
+    static QList<ComicItem *> *modelData(QSqlQuery &sqlquery);
 };
 };