Fix potential crash on windows if raw.FileNameLength exceeds syscall.MAX_PATH

[hu13]

What does this pull request do?

Fix #318.

Where should the reviewer start?

How should this be manually tested?

The crash only happens when we enable recursive watch on windows here: https://github.com/fsnotify/fsnotify/blob/master/windows.go#L350 by changing the argument flag from false to true.

Then if we create a really long filepath (see code snippet in #318), and begin watching on the first parent directory of that path and let the recursive watch propagates, fsnotify will crash.

panic: runtime error: slice bounds out of range

goroutine 765 [running, locked to thread]:

filesync_daemon/fsnotify.(*Watcher).readEvents(0xc000c78f40)

        /home/builder/go/src/filesync_daemon/fsnotify/windows.go:456 +0xfb1

created by filesync_daemon/fsnotify.NewWatcher

        /home/builder/go/src/filesync_daemon/fsnotify/windows.go:46 +0x21c

[mattn]

Thank you