fix: allow multiple weight mapping files for mistral

Downloading a Mistral model fails because it includes multiple weight
mapping files. The regression was introduced in commit
`766bee9f4a1fcb187fae543a525495d3ff482097`. I'm unclear on the original
intent, but perhaps the exception was meant to apply only to Granite
models. This isn’t an ideal fix, but it does enable Mistral to be
downloaded and used for chat.

Signed-off-by: Sébastien Han <seb@redhat.com>

Author: leseb

torchchat/cli/convert_hf_checkpoint.py

@@ -43,7 +43,8 @@ def convert_hf_checkpoint(
 
     # Load the json file containing weight mapping
     model_map_json_matches = [Path(m) for m in glob.glob(str(model_dir / "*.index.json"))]
-    assert len(model_map_json_matches) <= 1, "Found multiple weight mapping files"
+    if "mistral" not in model_name:
+        assert len(model_map_json_matches) <= 1, "Found multiple weight mapping files"
     if len(model_map_json_matches):
         model_map_json = model_map_json_matches[0]
     else: