Problem:
io_getevents() - read asynchronous I/O events from the completion
queue. For each IO event, the res field in io_event tells whether IO
event is succeeded or not. To see if the IO actually succeeded we
always need to check event.res (negative=error,
positive=bytesread/written).
LinuxAIOHandler::collect() doesn't check event.res value for each event.
which leads to incorrect value in n_bytes for IO context (or IO Slot).

Fix:
Added a check for event.res negative value.

RB: 20871
Reviewed by : annamalai.gurusami@oracle.com