message: Assert that IsComplete() in GetSpendData()
diff: @@ -504,6 +504,7 @@ WitnessV1Taproot TaprootBuilder::GetOutput() { return WitnessV1Taproot{m_output_
  TaprootSpendData TaprootBuilder::GetSpendData() const
  {
  + assert(IsComplete());
  TaprootSpendData spd;
  spd.merkle_root = m_branch.size() == 0 ? uint256() : m_branch[0]->hash;
  spd.internal_key = m_internal_key;
  