GP-0 fix unique file number generation for duplicate files

The size of the map was used as the unique id for file that didn't have
an explicit file number.  GP-4632 change accidentally disturbed this and
was creating filenames that didn't match previous logic.

Ghidra/Features/Base/src/main/java/ghidra/formats/gfilesystem/FileSystemIndexHelper.java

@@ -72,6 +72,7 @@ static class FileData<METADATATYPE> {
 	public FileSystemIndexHelper(GFileSystem fs, FSRLRoot fsFSRL) {
 		GFile rootGFile = GFileImpl.fromFSRL(fs, null, fsFSRL.withPath("/"), true, -1);
 		rootDir = new FileData<>(rootGFile, null, -1);
+		fileToEntryMap.put(rootDir.file, rootDir);
 		directoryToListing.put(rootDir.file, new HashMap<>());
 	}