patchsequencer: fix memory leak if `todo_list_rearrange_squash()` failed

> From: Lidong Yan <502024330056@smail.nju.edu.cn>
> 
> In sequencer.c:todo_list_rearrange_squash, if it fails, memory
> allocated in `next`, `tail`, `subjects` and `subject2item` will leak.
> Jump to cleanup label before return could fix this leak problem.

> Signed-off-by: Lidong Yan <502024330056@smail.nju.edu.cn>
> ---
>      sequencer: fix memory leak if todo_list_rearrange_squash() failed
>      
>      In sequencer.c:todo_list_rearrange_squash, if it fails, memory allocated
>      in next, tail, subjects and subject2item will leak. Jump to cleanup
>      label before return could fix this leak problem.
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1965%2Fbrandb97%2Ffix-sequencer-todo-leak-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1965/brandb97/fix-sequencer-todo-leak-v1
> Pull-Request: https://github.com/git/git/pull/1965
> 
>   sequencer.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/sequencer.c b/sequencer.c
> index b5c4043757e..5fb7b68a7ab 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -6596,6 +6596,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>   	char **subjects;
>   	struct commit_todo_item commit_todo;
>   	struct todo_item *items = NULL;
> +	int ret = 0;
>   
>   	init_commit_todo_item(&commit_todo);
>   	/*
> @@ -6626,8 +6627,8 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>   		}
>   
>   		if (is_fixup(item->command)) {
> -			clear_commit_todo_item(&commit_todo);
> -			return error(_("the script was already rearranged."));
> +			ret = error(_("the script was already rearranged."));
> +			goto cleanup;
>   		}
>   
>   		repo_parse_commit(the_repository, item->commit);
> @@ -6729,6 +6730,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>   		todo_list->items = items;
>   	}
>   
> +cleanup:
>   	free(next);
>   	free(tail);
>   	for (i = 0; i < todo_list->nr; i++)
> @@ -6738,7 +6740,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>   
>   	clear_commit_todo_item(&commit_todo);
>   
> -	return 0;
> +	return ret;
>   }
>   
>   int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
> 
> base-commit: 6f84262c44a89851c3ae5a6e4c1a9d06b2068d75

> 
> On 14/05/2025 14:53, Lidong Yan via GitGitGadget wrote:
>> From: Lidong Yan <502024330056@smail.nju.edu.cn>
>> In sequencer.c:todo_list_rearrange_squash, if it fails, memory
>> allocated in `next`, `tail`, `subjects` and `subject2item` will leak.
>> Jump to cleanup label before return could fix this leak problem.
> 
> You could mention that you're adding the cleanup label.

> On 14/05/2025 14:53, Lidong Yan via GitGitGadget wrote:
>> From: Lidong Yan <502024330056@smail.nju.edu.cn>
>> In sequencer.c:todo_list_rearrange_squash, if it fails, memory
>> allocated in `next`, `tail`, `subjects` and `subject2item` will leak.
>> Jump to cleanup label before return could fix this leak problem.
>
> You could mention that you're adding the cleanup label.
>
> I suspect reaching this condition is a bug as well because we should
> only rearrange the todo list when the rebase starts. However I'm not
> 100% sure that it is impossible to trigger this condition so lets free
> it as you suggest. The code changes look good.

>> @@ -6626,8 +6627,8 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>>   		}
>>     		if (is_fixup(item->command)) {
>> -			clear_commit_todo_item(&commit_todo);
>> -			return error(_("the script was already rearranged."));
>> +			ret = error(_("the script was already rearranged."));
>> +			goto cleanup;
>>   		}