refs: cover git_reference_name_to_oid() unfound behavior

tests-clar/refs/read.c

@@ -223,6 +223,7 @@ void test_refs_read__trailing(void)
 void test_refs_read__unfound_return_ENOTFOUND(void)
 {
 	git_reference *reference;
+	git_oid id;
 
 	cl_assert_equal_i(GIT_ENOTFOUND,
 		git_reference_lookup(&reference, g_repo, "TEST_MASTER"));
@@ -232,6 +233,9 @@ void test_refs_read__unfound_return_ENOTFOUND(void)
 		git_reference_lookup(&reference, g_repo, "refs/tags/test/master"));
 	cl_assert_equal_i(GIT_ENOTFOUND,
 		git_reference_lookup(&reference, g_repo, "refs/tags/test/farther/master"));
+
+	cl_assert_equal_i(GIT_ENOTFOUND,
+		git_reference_name_to_id(&id, g_repo, "refs/tags/test/farther/master"));
 }
 
 static void assert_is_branch(const char *name, bool expected_branchness)