Improve error propagation in shallow call

src/repository.c

@@ -2001,9 +2001,10 @@ int git_repository_is_shallow(git_repository *repo)
 	error = git_path_lstat(path.ptr, &st);
 	git_buf_free(&path);
 
-	if (error == GIT_ENOTFOUND)
+	if (error == GIT_ENOTFOUND) {
+		giterr_clear();
 		return 0;
-	if (error < 0)
-		return -1;
-	return st.st_size == 0 ? 0 : 1;
+	}
+
+	return error < 0 ? error : st.st_size == 0 ? 0 : 1;
 }

tests/repo/shallow.c

@@ -31,3 +31,9 @@ void test_repo_shallow__shallow_repo(void)
 	cl_assert_equal_i(1, git_repository_is_shallow(g_repo));
 }
 
+void test_repo_shallow__clears_errors(void)
+{
+	g_repo = cl_git_sandbox_init("testrepo.git");
+	cl_assert_equal_i(0, git_repository_is_shallow(g_repo));
+	cl_assert_equal_p(NULL, giterr_last());
+}