fix iterator overflow when gradient accumulation is 1
Author: winglian
Pull request: yes

# What does this PR do?

In the original part of the code:
```python
            epoch_iterator = iter(epoch_dataloader)
            # We chunkify the epoch iterator into gradient accumulation steps `n` batches
            remainder = num_examples % args.gradient_accumulation_steps
            if remainder == 0:
                remainder = args.gradient_accumulation_steps
            update_step = -1
            total_updates = steps_in_epoch // args.gradient_accumulation_steps + 1
```
if we assume `args.gradient_accumulation_steps` is `1` and the length of the iterator/`num_examples` is say `10`, then `N % 1` is always `remainder = 0`.
which then sets the `remainder` to an additional step.
Then for total updates, we know that it's `10 steps // 1 ga + 1`, so `total_updates = 11`, which is one more than the actual number of row in the dataset/dataloader.

then when the loop calls `self.get_batch_samples(epoch_iterator, num_batches)` on the `remainder` there is no data left, which I believe is causing a segmentation fault for me.


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Comments:
There is indeed an issue there. We can go with your solution or re-write this to make it easier to follow, something like this.
I'll let @muellerzr  decide. 

```python
remainder = num_examples % args.gradient_accumulation_steps

# Ensure that `remainder` logic doesn't add unnecessary steps
if remainder == 0:
    total_updates = steps_in_epoch // args.gradient_accumulation_steps
else:
    total_updates = steps_in_epoch // args.gradient_accumulation_steps + 1

update_step = -1

# Loop through the calculated total updates
for _ in range(total_updates):
    update_step += 1

    # Properly handle the last step with the remainder logic
    if update_step == (total_updates - 1) and remainder != 0:
        num_batches = remainder
    else:
        num_batches = args.gradient_accumulation_steps
```

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_35960). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

I like your solution much better.

> There is indeed an issue there. We can go with your solution or re-write this to make it easier to follow, something like this. I'll let @muellerzr decide.
> 
> ```python
> remainder = num_examples % args.gradient_accumulation_steps
> 
> # Ensure that `remainder` logic doesn't add unnecessary steps
> if remainder == 0:
>     total_updates = steps_in_epoch // args.gradient_accumulation_steps
> else:
>     total_updates = steps_in_epoch // args.gradient_accumulation_steps + 1
> 
> update_step = -1
> 
> # Loop through the calculated total updates
> for _ in range(total_updates):
>     update_step += 1
> 
>     # Properly handle the last step with the remainder logic
>     if update_step == (total_updates - 1) and remainder != 0:
>         num_batches = remainder
>     else:
>         num_batches = args.gradient_accumulation_steps
> ```