path: error out if the callback returns an error

When the callback returns an error, we should stop immediately. This
broke when trying to make sure we pass specific errors up the chain.

This broke cancelling out of the loose backend's foreach.

src/path.c

@@ -1066,8 +1066,10 @@ int git_path_direach(
 		git_buf_truncate(path, wd_len); /* restore path */
 
 		/* Only set our own error if the callback did not set one already */
-		if (error != 0 && !giterr_last()) {
+		if (error != 0) {
+			if (!giterr_last())
 				giterr_set_after_callback(error);
+
 			break;
 		}
 	}

tests/odb/foreach.c

@@ -71,15 +71,35 @@ static int foreach_stop_cb(const git_oid *oid, void *data)
 	return (*nobj == 1000) ? -321 : 0;
 }
 
+static int foreach_stop_first_cb(const git_oid *oid, void *data)
+{
+	int *nobj = data;
+	(*nobj)++;
+
+	GIT_UNUSED(oid);
+
+	return -123;
+}
+
 void test_odb_foreach__interrupt_foreach(void)
 {
 	int nobj = 0;
+	git_oid id;
 
 	cl_git_pass(git_repository_open(&_repo, cl_fixture("testrepo.git")));
 	git_repository_odb(&_odb, _repo);
 
 	cl_assert_equal_i(-321, git_odb_foreach(_odb, foreach_stop_cb, &nobj));
 	cl_assert(nobj == 1000);
+
+	git_odb_free(_odb);
+	git_repository_free(_repo);
+
+	cl_git_pass(git_repository_init(&_repo, "onlyloose.git", true));
+	git_repository_odb(&_odb, _repo);
+
+	cl_git_pass(git_odb_write(&id, _odb, "", 0, GIT_OBJ_BLOB));
+	cl_assert_equal_i(-123, git_odb_foreach(_odb, foreach_stop_first_cb, &nobj));
 }
 
 void test_odb_foreach__files_in_objects_dir(void)