Fix warnings with clang and a wrong type conversion.

  int error_threshold_for_merging = 1;

  bool is_merged = false;

  for (int si = 0; si < error_threshold_for_merging + 1; ++si) {

    int seed_start_position =

    size_t seed_start_position =

        negative_read2.find(read1 + si * seed_length, 0, seed_length);

    while ((uint32_t)seed_start_position != std::string::npos &&

    while (seed_start_position != std::string::npos &&

           read2_length - seed_start_position + seed_length * si >=

               (uint32_t)min_overlap_length &&

           seed_start_position >= si * seed_length) {

  uint64_t num_uniquely_mapped_reads_ = 0;

  uint64_t num_reads_ = 0;

  // # identical reads.

  uint64_t num_duplicated_reads_ = 0;

  // uint64_t num_duplicated_reads_ = 0;

  // For barcode stats.

  const uint64_t initial_num_sample_barcodes_ = 20000000;