message: fuzz: Improve coverage for CPartialMerkleTree fuzzing harness
diff: void test_one_input(const std::vector<uint8_t>& buffer)
  {
  FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
  - std::optional<CPartialMerkleTree> partial_merkle_tree = ConsumeDeserializable<CPartialMerkleTree>(fuzzed_data_provider);
  - if (!partial_merkle_tree) {
  - return;
  + CPartialMerkleTree partial_merkle_tree;
  + switch (fuzzed_data_provider.ConsumeIntegralInRange<int>(0, 1)) {
  + case 0: {
  + const std::optional<CPartialMerkleTree> opt_partial_merkle_tree = ConsumeDeserializable<CPartialMerkleTree>(fuzzed_data_provider);
  + if (opt_partial_merkle_tree) {
  + partial_merkle_tree = *opt_partial_merkle_tree;
  }
  - (void)partial_merkle_tree->GetNumTransactions();
  + break;
  + }
  + case 1: {
  + CMerkleBlock merkle_block;
  + const std::optional<CBlock> opt_block = ConsumeDeserializable<CBlock>(fuzzed_data_provider);
  + CBloomFilter bloom_filter;
  + std::set<uint256> txids;
  + if (opt_block && !opt_block->vtx.empty()) {
  + if (fuzzed_data_provider.ConsumeBool()) {
  + merkle_block = CMerkleBlock{*opt_block, bloom_filter};
  + } else if (fuzzed_data_provider.ConsumeBool()) {
  + while (fuzzed_data_provider.ConsumeBool()) {
  + txids.insert(ConsumeUInt256(fuzzed_data_provider));
  + }
  + merkle_block = CMerkleBlock{*opt_block, txids};
  + }
  + }
  + partial_merkle_tree = merkle_block.txn;
  + break;
  + }
  + }
  + (void)partial_merkle_tree.GetNumTransactions();
  std::vector<uint256> matches;
  std::vector<unsigned int> indices;
  - (void)partial_merkle_tree->ExtractMatches(matches, indices);
  + (void)partial_merkle_tree.ExtractMatches(matches, indices);
  }
  