Aleix authored Jan 11, 2017 and Brad King committed Jan 11, 2017

`cmsys::SystemTools::SplitPath` will return empty segments on paths
where there's duplicaded consequent slashes (e.g.  `/home/dir/my//stuff`).
This makes the cmFileWatcher choke.  Teach cmFileMonitor to skip these
empty segments.

Closes: #16531