tss2_pcrread: fix reading PCR 0
tss2_pcrread: fix reading PCR 0

The check if a PCR is set requires that the PCR value be greater than 0.
However, PCR index 0 is valid, so use another variable to track if the
PCR index is specified.
Similar to #2168

Fixes Error:
$ tss2_pcrread -x 0 -o -
No PCR index provided, use --pcrIndex
Usage: tss2_pcrread [<options>]

Fixes: #2167

Signed-off-by: Peter Huewe <761e034d6358ca9e0639fca07d0da47f2be745f2@infineon.com>

01org/tpm2.0-tools,01org/tpm2.0-tools,01org/tpm2.0-tools