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.

src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion_img2img.py

@@ -428,9 +428,6 @@ class StableDiffusionImg2ImgPipeline(DiffusionPipeline):
     def check_inputs(
         self, prompt, strength, callback_steps, negative_prompt=None, prompt_embeds=None, negative_prompt_embeds=None
     ):
-        if not isinstance(prompt, str) and not isinstance(prompt, list):
-            raise ValueError(f"`prompt` has to be of type `str` or `list` but is {type(prompt)}")
-
         if strength < 0 or strength > 1:
             raise ValueError(f"The value of strength should in [0.0, 1.0] but is {strength}")
 
@@ -623,7 +620,12 @@ class StableDiffusionImg2ImgPipeline(DiffusionPipeline):
         self.check_inputs(prompt, strength, callback_steps, negative_prompt, prompt_embeds, negative_prompt_embeds)
 
         # 2. Define call parameters
-        batch_size = 1 if isinstance(prompt, str) else len(prompt)
+        if prompt is not None and isinstance(prompt, str):
+            batch_size = 1
+        elif prompt is not None and isinstance(prompt, list):
+            batch_size = len(prompt)
+        else:
+            batch_size = prompt_embeds.shape[0]
         device = self._execution_device
         # here `guidance_scale` is defined analog to the guidance weight `w` of equation (2)
         # of the Imagen paper: https://arxiv.org/pdf/2205.11487.pdf . `guidance_scale = 1`