nvs: nvs_get_stats fixed test, improved comment

components/nvs_flash/src/nvs_pagemanager.cpp

@@ -235,6 +235,7 @@ esp_err_t PageManager::fillStats(nvs_stats_t& nvsStats)
     nvsStats.free_entries  += mFreePageList.size() * Page::ENTRY_COUNT;
 
     // calculate available entries from free entries by applying reserved page size
+    // avoid overflow of size_t declared available_entries in case of free_entries being too low
     nvsStats.available_entries = (nvsStats.free_entries >= Page::ENTRY_COUNT) ? nvsStats.free_entries - Page::ENTRY_COUNT : 0;
 
     return err;

components/nvs_flash/test_apps/main/test_nvs.c

@@ -314,7 +314,7 @@ TEST_CASE("calculate used and free space", "[nvs]")
     TEST_ASSERT_TRUE(stat1.total_entries == stat2.total_entries);
     TEST_ASSERT_TRUE(stat1.used_entries == 7);
 
-    TEST_ASSERT_TRUE(stat1.total_entries == (stat1.used_entries + stat1.free_entries + 126)); // one Page::ENTRY_COUNT is reserved
+    TEST_ASSERT_TRUE(stat1.total_entries == (stat1.used_entries + stat1.free_entries));
 
     // amount valid pair in namespace 2
     size_t h2_count_entries;