Query_cache::resize() frees memory containing active locks

[Vladislav Vaintroub]

Found when investigating Windows application verifier errors (application verifier is sort-of valgrind).

The callstack leading of "free" containing critical section is:
mysqld!free
  my_no_flags_free
  Query_cache::free_cache
  Query_cache::resize
  fix_query_cache_size
  set_var::update
  sql_set_variables
  mysql_execute_command
  mysql_parse

The callstack of critical section allocation is :
  pthread_cond_init
  my_rwlock_init
  Query_cache_query::init_n_lock
  Query_cache::store_query
  execute_sqlcom_select
  mysql_execute_command
  mysql_parse

Why freeing a heap block containing active critical section is bad
 - in the best case (the critical section is unlocked) it may lead to resource leakage, e.g underlying Windows event objects will be leaked.
- in the worst case (critical section is locked) it could lead to random hangs when the freed memory is again reused for another critical section

[Vladislav Vaintroub (wlad-montyprogram)]

Release in 5.2.7