[server] Fix potential crash when attempting to normalize module path

[rexxars]

Sometimes the hot module reloading cannot find a module in it's module map - when this happens the process-update script fails because it tries to split a string which is actually undefined. We only use this to display which modules have been updated, so it's non-critical that the path is correct.

This PR checks for this case and returns <unknown> should we not be passed a path name.