download_from_original_stable_diffusion_ckpt initializes correct default pipeline for SDXL

[lukas-kuhn]

What does this PR do?

Previously the download_from_original_stable_diffusion_ckpt function, when run with a SDXL model, would default to a StableDiffusionPipeline pipeline class. This would lead to downstream errors because the SDXL model has a text_encoder_2 which is not recognized in the StableDiffusionPipeline.

A few lines below, the function checks if the model is a SDXL or SDXL-Refiner and sets the model_type variable accordingly.

I moved the initialization of the default pipeline (when None is set specifically) below this detection if the model is SDXL or SDXL-Refiner and initialize the correct default pipeline. This makes it easier for users who for example run the convert_original_stable_diffusion_to_diffusers.py script.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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  This issue came to my attention only a few hours ago and I immediately fixed it but it was part of a discussion at Issue#4488. It basically adds a better default to MR#4461
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• Did you write any new necessary tests? Not necessary imo

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@patrickvonplaten @yiyixuxu

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[patrickvonplaten]

Nice refactor!