inotify: fix coalesce duplicate events into a single event in special case

If we do rename a dir entry, like this:

  rename("/tmp/ino7UrgoJ.rename1", "/tmp/ino7UrgoJ.rename2")
  rename("/tmp/ino7UrgoJ.rename2", "/tmp/ino7UrgoJ")

The duplicate events should be coalesced into a single event. But those two
events do not be coalesced into a single event, due to some bad check in
event_compare(). It can not match the two NULL inodes as the same event.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Eric Paris <eparis@redhat.com>