fix uninitialized variable in DateAddedFilterNode();

[daschuer]

this is a valgrind finding

==37336== Conditional jump or move depends on uninitialised value(s)
==37336==    at 0x499023A: DateAddedFilterNode::toSql() const (searchquery.cpp:916)
==37336==    by 0x4993CD4: AndNode::toSql() const (searchquery.cpp:123)
==37336==    by 0x499393C: OrNode::toSql() const (searchquery.cpp:147)
==37336==    by 0x4993CD4: AndNode::toSql() const (searchquery.cpp:123)
==37336==    by 0x48AA1ED: BaseTrackCache::filterAndSort(QSet<TrackId> const&, QString const&, QString const&, QString const&, QList<SortColumn> const&, int, QHash<TrackId, int>*) (basetrackcache.cpp:491)
==37336==    by 0x489448D: BaseSqlTableModel::select() (basesqltablemodel.cpp:287)
==37336==    by 0x46763E9: WTrackTableView::doSortByColumn(int, Qt::SortOrder) (wtracktableview.cpp:1658)
==37336==    by 0x4676DCC: WTrackTableView::loadTrackModel(QAbstractItemModel*, bool) (wtracktableview.cpp:339)
==37336==    by 0x4853094: DlgAnalysis::DlgAnalysis(WLibrary*, QSharedPointer<ConfigObject<ConfigValue> >, Library*) (dlganalysis.cpp:52)
==37336==    by 0x484D501: AnalysisFeature::bindLibraryWidget(WLibrary*, KeyboardEventFilter*) (analysisfeature.cpp:75)
==37336==    by 0x4377A18: Library::bindLibraryWidget(WLibrary*, KeyboardEventFilter*) (library.cpp:459)
==37336==    by 0x4A10D80: LegacySkinParser::parseLibrary(QDomElement const&) (legacyskinparser.cpp:1596)
==37336== 

[ronso0]

Indeed, thanks!

Can you take a look at #16047 ?