Fix:
===
Implemented upstream fix.

commit 7d3d0fc3
Author: He Zhenxing <zhenxing.he@sun.com>

Backport Bug#45852 Semisynch: Last_IO_Error: Fatal error: Failed
to run 'after_queue_event' hook

Errors when send reply to master should never cause the IO thread
to stop, because master can fall back to async replication if it
does not get reply from slave.

The problem is fixed by deliberately ignoring the return value of
slave_reply.