Reuse iterators in bench

Bench.cpp

@@ -92,9 +92,9 @@ void bulkFirstGeq() {
     keys[i].len = sizeof(bigEndian);
   }
 
+  weaselab::VersionedMap::Iterator iterators[kNumQueries];
   // Bench
   bench.run("bulkFirstGeq", [&] {
-    weaselab::VersionedMap::Iterator iterators[kNumQueries];
     versionedMap.firstGeq(keys, versions, iterators, kNumQueries);
   });
 }