Some multibyte sequences could be considered by my_mbcharlen() functions
as multibyte character but more exact my_ismbchar() does not think so.
In such a case this multibyte sequences is pushed into 'stack' buffer which
is too small to accommodate the sequence.
The fix is to allocate stack buffer in
compliance with max character length.


mysql-test/r/loaddata.result:
  test case
mysql-test/t/loaddata.test:
  test case
sql/sql_load.cc:
  allocate stack buffer in compliance with max character length.