Add support for external latent specification

[gordicaleksa]

https://colab.research.google.com/github/pcuenca/diffusers-examples/blob/main/notebooks/stable-diffusion-seeds.ipynb <- this notebook (linked in the README) makes it seem as if we can specify the latent externally, but looking at the code that doesn't seem to work.

Here is a proposed tweak (comment on karpathy's gist, some asserts are needed)

[pcuenca]

Hi Aleksa, thanks for writing!

That notebook relies on PR #247, which was recently merged. It should work with the main branch of diffusers, but not yet with the latest PyPi version (0.2.4). Could you please try with main instead? If it still doesn't work, please do let us know! :)

Thanks again!

[gordicaleksa]

Hi Pedro!

Thanks for the quick reply!

Ah, ok, I'm on the older version apparently recommended for stable diffusion (0.2.4) so I missed this one! LGTM!