iocp: fix crash, GetQueuedCompletionStatus() write freed WSAOVERLAPPED memory

[jimying]

try to fix issue #985

[nanangizz]

Great! I assume you've tested this and it does fix the issue :)

I think we also need to run under somekind of stress test, e.g: using ioqueue test in pjlib-test, to make sure all memory pools (of pending ops) are properly released. Note that the after an ioqueue key is unregistered, the key will be put into the closing-key-list and soon into the free-key-list to be reused by another socket. We need to make sure that all pending op has been freed before the key is freed & reused.

Next, perhaps we can apply a little bit optimization, e.g: instead of mem-pool for each pending-op, perhaps mem-pool per ioqueue-key to avoid multiple alloc+free for multiple pending-op, using same mechanism as ioqueue key (employing additional list for keeping unused pending-op instances to be reused later).

[jimying]

Note:
this only fix the issue when PJ_IOQUEUE_HAS_SAFE_UNREG=1;
PJ_IOQUEUE_HAS_SAFE_UNREG=0 still has memory error