[From Single File] Force accelerate to be installed (huggingface#4078)

force accelerate to be installed

Author: patrickvonplaten

src/diffusers/pipelines/stable_diffusion/convert_from_ckpt.py

@@ -1172,6 +1172,11 @@ def download_from_original_stable_diffusion_ckpt(
         StableUnCLIPPipeline,
     )
 
+    if not is_accelerate_available():
+        raise ImportError(
+            "To correctly use `from_single_file`, please make sure that `accelerate` is installed. You can install it with `pip install accelerate`."
+        )
+
     if pipeline_class is None:
         pipeline_class = StableDiffusionPipeline