- Fix https://stackoverflow.com/questions/60625778/import-complex-xml-from-multiple-files-in-mariadb/60637429#60637429
  Import complex XML from multiple files in MariaDB
  Some row results are missing and replaced by the last file one.
  Thats because Nx and Sx column members are not reset when changing file.
  modified:   storage/connect/tabxml.cpp
  modified:   storage/connect/tabxml.h