Avoid buffer overflow in asn1_parse2

Avoid buffer overflow in asn1_parse2

asn1_par.c r1.29 changed to access p[0] directly, and this pointer could be
overrun since ASN1_get_object advances pointer to the first content octet.
In case invalid ASN1 Boolean data, it has length but no content, I thought
this could be happen.
Adding check p with tot (diff below) will avoid this failure.

Reported by oss-fuzz 43633 and 43648(later)

ok tb@