message: Avoid performing arithmetic on nullptr in utf8proc
diff: @@ -450,8 +450,8 @@ static utf8proc_ssize_t seqindex_write_char_decomposed(utf8proc_uint16_t seqinde
  }
  for (; len >= 0; entry++, len--) {
  utf8proc_int32_t entry_cp = seqindex_decode_entry(&entry);
  -
  - written += utf8proc_decompose_char(entry_cp, dst+written,
  + utf8proc_int32_t *dst_ptr = dst ? dst + written : nullptr;
  + written += utf8proc_decompose_char(entry_cp, dst_ptr,
  (bufsize > written) ? (bufsize - written) : 0, options,
  last_boundclass);
  if (written < 0) return UTF8PROC_ERROR_OVERFLOW;
  @@ -624,8 +624,9 @@ UTF8PROC_DLLEXPORT utf8proc_ssize_t utf8proc_decompose_custom(
  if (custom_func != NULL) {
  uc = custom_func(uc, custom_data); /* user-specified custom mapping */
  }
  + utf8proc_int32_t *target_buffer = buffer ? buffer + wpos : nullptr;
  decomp_result = utf8proc_decompose_char(
  - uc, buffer + wpos, (bufsize > wpos) ? (bufsize - wpos) : 0, options,
  + uc, target_buffer, (bufsize > wpos) ? (bufsize - wpos) : 0, options,
  &boundclass
  );
  if (decomp_result < 0) return decomp_result;
  