public boolean containsFile(String fileName) throws IOException {
		synchronized (fileSystem) {
			if (fileDataCache.containsKey(fileName)) {
				return true;
			}
			if (visited) {
				return false;
			}
			return addFileData(fileName) != null;
		}
	}
Check for existence of file.  If folder previously visited, rely on fileDataCache
@param fileName the name of the file to look for
@return true if this folder contains the fileName, else false
@throws IOException if an IO error occurs while checking for file existance
Ghidra/Framework/Project/src/main/java/ghidra/framework/data/GhidraFolderData.java