message: Bugfix: make ToPrivateString work with x-only keys
diff: @@ -259,7 +259,15 @@ public:
  bool ToPrivateString(const SigningProvider& arg, std::string& ret) const override
  {
  CKey key;
  - if (!arg.GetKey(m_pubkey.GetID(), key)) return false;
  + if (m_xonly) {
  + for (const auto& keyid : XOnlyPubKey(m_pubkey).GetKeyIDs()) {
  + arg.GetKey(keyid, key);
  + if (key.IsValid()) break;
  + }
  + } else {
  + arg.GetKey(m_pubkey.GetID(), key);
  + }
  + if (!key.IsValid()) return false;
  ret = EncodeSecret(key);
  return true;
  }
  