Checking for QT_CONFIG(printdialog) is not enough when printsupport is
completely disabled since then the macro will throw an error. Therefore
add an additional check 'defined(QT_PRINTSUPPORT_LIB)' before using the
QT_CONFIG macro.
Fixes: QTBUG-81626
Change-Id: Ie9898f057cdd6bf9daf4ba9135987cb6e901e7bf
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>