ReadPCRs returns empty map without error when using SHA256

Hi Team

I was using tpm2.ReadPCRs on a hardware tpm with the following PCRSelection:
`{11 [0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23]}`
This return an empty map without an error:
```read PCRs: map[]```
However when I using SHA1
`{4 [0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23]}`
it works.

Can someone please help with some suggestions? Thanks!

I am using centos7 on Dell R640

Start at the tpm2.ReadPCRs entry point and compare its SHA256 PCRSelection handling with the working SHA1 case. Reproduce the empty-map result on the reported TPM setup, then verify that SHA256 returns PCR data or a clear error and add regression coverage if the repository has an appropriate test location.

Written by the indexing model from the issue text.