[2436] Use a reference

According to the standard, it is safe here. So we save ourselves a copy.

src/lib/datasrc/zone_loader.cc

@@ -150,8 +150,8 @@ ZoneLoader::loadIncremental(size_t limit) {
     if (complete_) {
         // Everything is loaded. Perform some basic sanity checks on the zone.
         RRsetCollection collection(updater_);
-        const dns::Name zone_name(updater_->getFinder().getOrigin());
-        const dns::RRClass zone_class(updater_->getFinder().getClass());
+        const dns::Name& zone_name(updater_->getFinder().getOrigin());
+        const dns::RRClass& zone_class(updater_->getFinder().getClass());
         const dns::ZoneCheckerCallbacks
             callbacks(boost::bind(&logError, &zone_name, &zone_class, _1),
                       boost::bind(&logWarning, &zone_name, &zone_class, _1));