Fix possible circular notification

Author: lballabio

ql/termstructures/yield/oisratehelper.cpp

@@ -51,6 +51,10 @@ namespace QuantLib {
 
         overnightIndex_ =
             ext::dynamic_pointer_cast<OvernightIndex>(overnightIndex->clone(termStructureHandle_));
+        // We want to be notified of changes of fixings, but we don't
+        // want notifications from termStructureHandle_ (they would
+        // interfere with bootstrapping.)
+        overnightIndex_->unregisterWith(termStructureHandle_);
 
         registerWith(overnightIndex_);
         registerWith(discountHandle_);
@@ -161,6 +165,10 @@ namespace QuantLib {
 
         auto clonedOvernightIndex =
             ext::dynamic_pointer_cast<OvernightIndex>(overnightIndex->clone(termStructureHandle_));
+        // We want to be notified of changes of fixings, but we don't
+        // want notifications from termStructureHandle_ (they would
+        // interfere with bootstrapping.)
+        clonedOvernightIndex->unregisterWith(termStructureHandle_);
 
         registerWith(clonedOvernightIndex);
         registerWith(discountHandle_);