[core][fix] Multipart name (#2203)

Author: aquamatthias

fixcore/fixcore/web/api.py

@@ -1389,7 +1389,7 @@ async def write_files(mpr: MultipartReader, tmp_dir: str) -> Dict[str, str]:
                 if isinstance(part, MultipartReader):
                     files.update(await write_files(part, tmp_dir))
                 elif isinstance(part, BodyPartReader):
-                    name = part.filename
+                    name = part.name
                     if not name:
                         raise AttributeError("Multipart request: content disposition name is required!")
                     path = os.path.join(tmp_dir, rnd_str())  # use random local path to avoid clashes