Fix false positive on res_stats checking in cache unit test

Utility function expectCacheStats() falsely pass while 'stats' is empty
in input parameter and not empty in cache.

Bug: 134897288
Change-Id: Ib623157301c01cffadc3c6db2c8e7c7146edeb13
diff --git a/resolv_cache_unit_test.cpp b/resolv_cache_unit_test.cpp
index 9f4d0af..997a58a 100644
--- a/resolv_cache_unit_test.cpp
+++ b/resolv_cache_unit_test.cpp
@@ -215,6 +215,11 @@
         EXPECT_TRUE(params == expected.setup.params) << msg;
 
         // res_stats checking.
+        if (expected.stats.size() == 0) {
+            for (int ns = 0; ns < nscount; ns++) {
+                EXPECT_EQ(0U, stats[ns].sample_count) << msg;
+            }
+        }
         for (size_t i = 0; i < expected.stats.size(); i++) {
             EXPECT_TRUE(stats[i] == expected.stats[i]) << msg;
         }