Problem: there is an ASSERT() in the Log_event::read_log_event() checking the integrity 
of the event's data that may fail.
Fix: move the assert's condition to an explicit check.


mysql-test/r/ctype_cp932_binlog_stm.result:
  Fix for bug #28436: Incorrect position in SHOW BINLOG EVENTS causes server coredump
    - test result.
mysql-test/t/ctype_cp932_binlog_stm.test:
  Fix for bug #28436: Incorrect position in SHOW BINLOG EVENTS causes server coredump
    - test case.
sql/log_event.cc:
  Fix for bug #28436: Incorrect position in SHOW BINLOG EVENTS causes server coredump
    - assert's condition moved to the explicit integrity check.