PVS-Studio warning V527 for PNG library

png_size_t /* PRIVATE */
png_check_keyword(png_structp png_ptr, png_charp key,
                  png_charpp new_key)
{
  ...
  if (key_len > 79)
  {
    png_warning(png_ptr,
                "keyword length must be 1 - 79 characters");
    new_key[79] = '\0';
    key_len = 79;
  }
  ...
}

This is what should have been written here: (*new_key)[79] = '\0';

This suspicious code was found in PNG library project by PVS-Studio static code analyzer.
Warning message is:
V527 It is odd that the '\0' value is assigned to 'char' type pointer. Probably meant: *new_key [79] = '\0'. graphics3D pngwutil.c 1283

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