[CRASH] QSortFilterProxyModel crash

Steps to reproduce / test case:

If you set as a source model a QSqlQueryModel which has no query set yet (or any other empty model, I assume), and then use setHeaderData() on the source model, the application crashes.

Example code:

#include <QApplication>
#include <QSqlQueryModel>
#include <QSortFilterProxyModel>

// connection.h from Qt/examples/sql
#include "../connection.h"

int main(int argc, char *argv[])
{
QApplication app(argc, argv);
if (!createConnection())
return 1;

QSqlQueryModel plainModel;
QSortFilterProxyModel proxyModel;
proxyModel.setSourceModel(&plainModel);

// next line causes the crash
plainModel.setHeaderData(0, Qt::Horizontal, QObject::tr("ID"));

// setting the query before the header data works...
plainModel.setQuery("select * from person");
plainModel.setHeaderData(0, Qt::Horizontal, QObject::tr("ID"));

return 0;
}

More information:

The attached image shows where the crash occurs. No validation is done before accessing the vector.