Enlarge _oid2txt buffer to handle larger OIDs (#3612)

The OpenSSL manual recommends a buffer size of 80 for OBJ_oid2txt:
https://www.openssl.org/docs/crypto/OBJ_nid2ln.html#return_values.
But OIDs longer than this occur in real life (e.g. Active Directory
makes some very long OIDs).  If the length of the stringified OID
exceeds the buffer size, allocate a new buffer that is big enough to
hold the stringified OID, and re-do the conversion into the new
buffer.
4 files changed