unittest: add an assert for chain_listxattr.

As there is no assert after chain_listxattr(), and memset actual to '\0'
immediately, we did not test chain_listxattr() at all.

This patch add an assert to do the unittest for chain_listxattr().

Signed-off-by: Dongsheng Yang <dongsheng.yang@easystack.cn>

src/test/objectstore/chain_xattr.cc

@@ -240,6 +240,7 @@ TEST(chain_xattr, listxattr) {
   char* actual = (char*)calloc(1, buffer_size);
   ASSERT_LT(buffer_size, chain_listxattr(file, NULL, 0)); // size evaluation is conservative
   chain_listxattr(file, actual, buffer_size);
+  ASSERT_EQ(0, ::memcmp(expected, actual, buffer_size));
   ::memset(actual, '\0', buffer_size);
   chain_flistxattr(fd, actual, buffer_size);
   ASSERT_EQ(0, ::memcmp(expected, actual, buffer_size));