GeezerVison

This fixes #49562

Without this change, the provided test fails with 'passed a null parameter', telling you nothing about what's actually wrong (since no nulls are present in this test code).

With this change, the test correctly receives a 'Unable to load private key from PFX data' error, telling you exactly what's wrong.

I've also covered the cert case here. I have confirmed that the same 'null parameter' error would be unhelpfully thrown if cert was null, so I think that's similarly useful. I'm not sure how to actually produce a pfx that would trigger this, so I haven't included a test, and it's possible that this isn't a possible condition (i.e. maybe PKCS12_parse would fail in that case) but it seems likely that it's technically possible and worth covering, and it's very easy to do so.