swh.loader.pypi.model: Skip when no release is defined

swh/loader/pypi/model.py

@@ -106,6 +106,8 @@ class PyPiProject:
             # FIXME: there can be multiple 'package_type' here:
             # sdist, bdist_egg, bdist_wheel
             if isinstance(release, list):
+                if not release:
+                    continue
                 if len(release) > 1:
                     raise ValueError(
                         'Unsupported other formats for now, failing!')