AsyncMessenger: fix the leak of file_events

Signed-off-by: Kefu Chai <tchaikov@gmail.com>
AsyncMessenger: reset newly allocated file_events

* otherwise there is chance that Event could take them as already
  initialized ones even they are filled with random bits from heap.
Merge pull request #3255 from tchaikov/async-leak

AsyncMessenger: fix the leak of file_events