private VersionFile getVersionFile(int vfIndex) throws IOException {
		if (openFileIx != vfIndex) {
			versionFiles[openFileIx].close();	
			openFileIx = vfIndex;
			versionFiles[openFileIx].open();
		}
		return versionFiles[openFileIx];
	}
Returns the list of free indexes associated with the original
buffer file.
Ghidra/Framework/DB/src/main/java/db/buffers/VersionFileHandler.java