Add a check in EC_Group encoding for OID being set
Add a check in EC_Group encoding for OID being set

Otherwise encoding would fail with an obtuse error message.

randombit/botan,Rohde-Schwarz-Cybersecurity/botan,webmaster128/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,webmaster128/botan,randombit/botan,webmaster128/botan,webmaster128/botan,Rohde-Schwarz-Cybersecurity/botan,randombit/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,webmaster128/botan,randombit/botan,randombit/botan