Fixes prompt input checks in StableDiffusion img2img pipeline (#2206)
* Fixes prompt input checks in img2img
Allows providing prompt_embeds instead of the prompt, which is not currently possible as the first check fails.
This becomes the same as the function found in https://github.com/huggingface/diffusers/blob/8267c7844504b55366525169187767ef92d1f499/src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion.py#L393
* Continues the fix
This also needs to be fixed. Becomes consistent with https://github.com/huggingface/diffusers/blob/8267c7844504b55366525169187767ef92d1f499/src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion.py#L558
I've now tested this implementation, and it produces the expected results.