Relax VendorPatchLevel Parsing

[JesusMcCloud]

The Vendor Patch Level contains the string "0" on the emulator, running Android 14.0.
Obviously, this is not compliant, but everybody working longer than five minutes with android key attestation knows that vendors can get even more "creative" than this

I therefore propose to make VendorPatchLevel an optional attribute. As far as I can tell from the source code, the actual value of this property is eagerly initialized on parsing, even if it is never accessed. Hence parsing fails and no verification whatsoever is possible, even if no checks for the vendor patch level are performed.

If this is fine, I'm happy to open a pull request.
First, however, we should evaluate how relaxed we really want to be, because I'd then extend my PR to more properties.

[JesusMcCloud]

This is hitting in production (yes, yes, I know this project was downgraded to "sample code only", but still)