can't parse relative paths "higher" than 3 levels up

When trying to LOAD DATA LOCAL INFILE using a relative path with 3 or
more levels up in the directory hierarchy, mysqld wrongly parses 
the path and as a consequence, can't find the file.

This bug was introduced by patch for bug#58205.
The reason for bug is that implementaiton of function cleanup_dirname()
doesn't take into account the begin of buffer being processed during
handling of path to file.


mysys/mf_pack.c:
  function cleanup_dirname() was modified: fixed wrong comparison
  condition when handling substring "../" at the begining of the buffer.