Fix minor performance issue with leak checker destroy (#401)

Signed-off-by: Neil R. Spruit <neil.r.spruit@intel.com>

Author: nrspruit

source/layers/validation/checkers/basic_leak/zel_basic_leak_checker.cpp

@@ -293,7 +293,7 @@ namespace validation_layer
             auto &dtors = s.dtors;
             int64_t diff = 0;
             for (size_t i = 0; i < ctors.size(); i++) {
-                auto name = ctors[i];
+                const auto& name = ctors[i];
                 auto zeCount = counts[name].load();
                 diff += zeCount;