Previously, a test exercising the X.509 CRT parser's behaviour
on unexpected tags would use a '00' byte in place of the tag
for the expected structure. This makes reviewing the examples
harder because the binary data isn't valid DER-encoded ASN.1.
This commit uses the ASN.1 NULL TLV '05 00' to test invalid
tags, and adapts surrounding structures' length values accordingly.
This eases reviewing because now the ASN.1 structures are still
well-formed at the place where the mismatch occurs.
0f5acc18c5