Fix windows dll context manager (#1120)

Author: NicolasHug

src/torchcodec/_core/ops.py

@@ -88,20 +88,19 @@ def load_torchcodec_shared_libraries() -> tuple[int, str]:
     )
 
 
+expose_ffmpeg_dlls = nullcontext
 if sys.platform == "win32" and hasattr(os, "add_dll_directory"):
     # On windows we try to locate the FFmpeg DLLs and temporarily add them to
     # the DLL search path. This seems to be needed on some users machine, but
     # not on our CI. We don't know why.
     if ffmpeg_path := shutil.which("ffmpeg"):
 
-        def cm():  # noqa: F811
+        def expose_ffmpeg_dlls():  # noqa: F811
             ffmpeg_dir = Path(ffmpeg_path).parent
             return os.add_dll_directory(str(ffmpeg_dir))  # that's the actual CM
 
-else:
-    cm = nullcontext
 
-with cm():
+with expose_ffmpeg_dlls():
     ffmpeg_major_version, core_library_path = load_torchcodec_shared_libraries()