[pipeline utils] sanitize pretrained_model_name_or_path (#5173)

Make sure the repo_id is valid before sending it to huggingface_hub to get a more understandable error message.

Re #5110
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

src/diffusers/pipelines/pipeline_utils.py

@@ -1033,6 +1033,10 @@ class DiffusionPipeline(ConfigMixin, PushToHubMixin):
         # 1. Download the checkpoints and configs
         # use snapshot download here to get it working from from_pretrained
         if not os.path.isdir(pretrained_model_name_or_path):
+            if pretrained_model_name_or_path.count("/") > 1: 
+                raise ValueError(                                                                                                                                                                                                          
+                   f"The provided pretrained_model_name_or_path \"{pretrained_model_name_or_path}\""
+                   " is neither a valid local path nor a valid repo id. Please check the parameter.")
             cached_folder = cls.download(
                 pretrained_model_name_or_path,
                 cache_dir=cache_dir,