lib/x509: use common routine for parsing data version

lib/x509: use common routine for parsing data version

OSS Fuzzer noted an issue in parsing (incorrect) CRL files with
zero-length version field. Certificate parser does not have this issue,
while CRL and OCSP Request and Response parsers shows this problem. To
remove code duplication extract common function and use it from all four
parsers.

Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>