Null exception occured when click on Luke desktop browser button

### Description

When I have set my share folder (luncene data) on window,I found that Luke desktop's path browser button occurd null exception.
like path \\xxx.xxx.xx.xx\trace . Finally I debug the source code and repair this bug as follow:
java file:OpenIndexDialogFactory.java
function:getLastOpenedDirectory

error:path.getParent()

repair:
```
private File getLastOpenedDirectory() {
List history = prefs.getHistory();
if (!history.isEmpty()) {
Path path = Paths.get(history.get(0));
if (Files.exists(path)) {
if(path.getParent() != null) {
return path.getParent().toAbsolutePath().toFile();
}else {
return path.toAbsolutePath().toFile();
}
}
}
return null;
}
```

### Version and environment details

Luncene 8.11.2 and I have check the newest version code has the same problem.

Open OpenIndexDialogFactory.java and inspect getLastOpenedDirectory, especially the path.getParent() handling for the reported network share path. Reproduce the Luke desktop browser-button flow with a path like \\xxx.xxx.xx.xx\trace, then run the relevant Luke tests if available. Done means the button no longer raises a null exception and still returns a usable directory.

Written by the indexing model from the issue text.