QPR-12200 flat forward curve shouldn't have a max date

Author: damienbarker

QuantExt/qle/termstructures/flatforwarddividendcurve.cpp

@@ -21,8 +21,7 @@
 namespace QuantExt {
 
 Date FlatForwardDividendCurve::maxDate() const { 
-	return dividendCurve_->maxDate(); 
-}
+	return Date::maxDate(); }
 
 DiscountFactor FlatForwardDividendCurve::discountImpl(Time t) const {
     Time maxTime = dividendCurve_->maxTime();