ZWJ is not supported properly

ZWJ is not supported properly (in some cases at least)
Steps to reproduce / test case

1. include <QtCore/QtCore>
2. include <QtGui/QtGui>
   int main ( int argc, char * argv [] )
   {
   QApplication app ( argc, argv ) ;
   QLabel * label = new QLabel ;
   label -> setText ( QString ( QChar ( 0x096B ) ) + QChar ( 0x200D ) + QChar ( 0x0903 ) ) ;
   label -> show () ;
   return app . exec () ;
   }

The expected behaviour is for the visarga sign (0x0903) to be placed immediately after the digit 5 (0x096B) by virtue of the zero width joiner (0x200D) – but it does not. Thw ZWJ is meant to request joining of things that are not normally joined. Normally the visarga sign 0x0903 would not be attached to the digit, but here the user has requested it (as this sequence is required for the writing of Vedic Sanskrit) and Qt does not render it properly.