sometimes `mysqldump --hex-blob' overruned output buffer by '\0' byte.

The dump_table() function has been fixed to reserve 1 byte more for the
last '\0' byte of dumped string.


client/mysqldump.c:
  Fixed bug #28522.
  The dump_table() function has been fixed to reserve 1 byte more for the
  last '\0' byte of dumped string.
mysql-test/t/mysqldump.test:
  Updated test case for bug #28522.
mysql-test/r/mysqldump.result:
  Updated test case for bug #28522.