CCBC-147 Fixed illegal memory access in win32 plugin

It isn't allowed to dereference event after calling the handler

Change-Id: I7d01ab33aa7af3f96e605a87a113cfdbaf05e41e
Reviewed-on: http://review.couchbase.org/24451
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>