packaging (and therefore pex) chokes on empty tags

`openturns==1.22` has a WHEEL file with an empty compatibility tag: ``` $ curl -LO https://files.pythonhosted.org/packages/16/a5/292e09768cdf1bae13bf94fae569d3b6bb9f2fceeecad336ae89aa9927ad/openturns-1.22-cp312-cp312-manylinux2014_x86_64.manylinux_2_17_x86_64.whl && unzip openturns-1.22-cp312-cp312-manylinux2014_x86_64.manylinux_2_17_x86_64.whl openturns-1.22.dist-info/WHEEL && cat openturns-1.22.dist-info/WHEEL ... Wheel-Version: 1.0 Generator: custom Root-Is-Purelib: false Tag: Tag: -manylinux_2_17_x86_64 Tag: -manylinux2014_x86_64 ``` Leading to: ``` $ python -m pex -v openturns==1.22 <snip> File "/Users/benjyw/src/pex/pex/wheel.py", line 265, in iter_compatible_python_versions for tag in self.metadata.tags: ^^^^^^^^^^^^^^^^^^ File "/Users/benjyw/src/pex/pex/wheel.py", line 110, in tags return tuple( ^^^^^^ File "/Users/benjyw/src/pex/pex/wheel.py", line 120, in <genexpr> sorted(tags.parse_tag(tag), key=lambda tag: str(tag)) ^^^^^^^^^^^^^^^^^^^ File "/Users/benjyw/src/pex/pex/vendor/_vendored/packaging_26_0/packaging/tags.py", line 112, in parse_tag interpreters, abis, platforms = tag.split("-") ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ValueError: not enough values to unpack (expected 3, got 1) ```