Support reinstantiating OPTIONAL entries

Description of problem:

It is not possible to reinstantiate deleted OPTIONAL field. It does not matter, why the field is deleted: because corresponding field was missing from parsed file or because it was explicitly deleted by asn1_write_value call.

Version of libtasn1 used:

4.16

Distributor of libtasn1 (e.g., Ubuntu, Fedora, RHEL)

Debian

How reproducible:

Steps to Reproduce:

  • delete the OPTIONAL field
  • try readding it

Actual results:

Expected results: