Merge branch 'QPR-9981_rebased' into 'master'

QPR-9981 bugfix interpolated inflation curve

Closes QPR-9981

See merge request qs/quantlib!31

Author: pcaspers

ql/termstructures/inflation/inflationhelpers.cpp

@@ -46,7 +46,7 @@ namespace QuantLib {
 
         std::pair<Date, Date> limStart = inflationPeriod(maturity_ - swapObsLag_, zii_->frequency());
 
-        if (detail::CPI::effectiveInterpolationType(zii_, observationInterpolation_) == CPI::Linear) {
+        if ((detail::CPI::effectiveInterpolationType(zii_, observationInterpolation_) == CPI::Linear) && (maturityDate_ != limStart.first)) {
             // if interpolated, we need to cover the end of the interpolation period
             earliestDate_ = limStart.first;
             latestDate_ = limStart.second + 1;