Add check for `target_sizes is None` in `post_process_image_guided_detection` for owlv2
Author: catalys1
Pull request: yes

Updates the `Owlv2ImageProcessor.post_process_image_guided_detection` by adding check for when `target_sizes is None`, as is done in the analogous function `post_process_detection`.

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Fixes #31915 


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Comments:
Hi @catalys1,
Thanks a lot for reporting the issue and submitting the fix! 🤗 

Can you, please, make a few more steps to finish this PR?

1) Method, modified in PR is a copy of the method from OwlViTImageProcessor, can you please make the same modifications to the original method and then run `make fix-copies` to make sure both methods are consistent?

On the top of the method you can see:
```python
# Copied from transformers.models.owlvit.image_processing_owlvit.OwlViTImageProcessor.post_process_image_guided_detection
```

2) run `make modified_only_fixup` - this will check  formatting and fix quality errors 

Thanks!


Done

I made those fixes