qt5: fix build

Add missing header after 60a23d5d

Change-Id: Ic24a78db3b425966e49fec96160d10670f68dea4

vcl/inc/qt5/Qt5FilePicker.hxx

@@ -39,6 +39,8 @@
 #include <QtCore/QHash>
 #include <QtWidgets/QFileDialog>
 
+#include <memory>
+
 class QGridLayout;
 class QLabel;
 class QWidget;