boolean containsFolder(String folderName) throws IOException {
		synchronized (fileSystem) {
			if (folderDataCache.containsKey(folderName)) {
				return true;
			}
			if (visited) {
				return folderList.contains(folderName);
			}
			return addFolderData(folderName) != null;
		}
	}
Check for existence of subfolder.  If this folder has previously been visited, 
rely on the cached folderList.
@param folderName name of folder to look for
@return true if folder exists, else false
@throws IOException if an IO error occurs when checking for folder's existance.
Ghidra/Framework/Project/src/main/java/ghidra/framework/data/GhidraFolderData.java