Merge "Fixed segmentation fault caused by fix of bug 568592"

common/Quadruple.cc

@@ -431,7 +431,9 @@ void QuadSet::add(QuadInterval* interval) {
         if (it == set)
           set = it->next;
         quadset_node_t* p = it;
-        it_old->next = it->next;
+        if (it_old != 0) {
+          it_old->next = it->next;
+        }
         it = it->next;
         delete p;
         continue;