windows: protect access to isClosed with mutex (#454)
windows: protect access to isClosed with mutex (#454)

isClosed may be read and modified concurrently if the Windows Watcher is
closed at the same time as a new entry being added. This change protects
isClosed to prevent race conditions.

The order of fields for the Windows Watcher have been rearranged to
group fields protected by the mutex together.
fsnotify/fsnotify,fsnotify/fsnotify,fsnotify/fsnotify