message: fix compile issue for some platforms
diff: @@ -203,7 +203,7 @@ DoubleSpendProof::Validity DoubleSpendProof::validate() const
  prevOutScript = output.scriptPubKey;
  } else {
  Coin coin;
  - if (!pcoinsTip->GetCoin({m_prevTxId, m_prevOutIndex}, coin)) {
  + if (!pcoinsTip->GetCoin({m_prevTxId, (uint32_t)m_prevOutIndex}, coin)) {
  /* if the output we spend is missing then either the tx just got mined
  * or, more likely, our mempool just doesn't have it.
  */
  @@ -221,7 +221,7 @@ DoubleSpendProof::Validity DoubleSpendProof::validate() const
  CTransaction tx;
  {
  READLOCK(mempool.cs_txmempool);
  - auto it = mempool.mapNextTx.find({m_prevTxId, m_prevOutIndex});
  + auto it = mempool.mapNextTx.find({m_prevTxId, (uint32_t)m_prevOutIndex});
  if (it == mempool.mapNextTx.end() || m_prevOutIndex >= it->second.ptx->vout.size()) {
  return MissingTransaction;
  }
  