The bug was that when using bulk insert combined with lock table, we intitalized the io cache with the wrong file position.
This fixed a bug where MariaDB could not read in a table dump done with mysqldump.


mysql-test/suite/maria/r/locking.result:
  Test case for locking + write cache bug
mysql-test/suite/maria/t/locking.test:
  Test case for locking + write cache bug
storage/maria/ma_extra.c:
  Initialize write cache used with bulk insert to correct file length.
  (The old code didn't work if one was using LOCK TABLE for the given table).