(1) The ZipFile methods getEntry(String) continues to work and should
not after ZipFile.close().
(2) The ZipFile methods getInputStream(ZipEntry), entries(),
read(long,byte,int,int), and read(long) get NullPointer exceptions
when used after ZipFile.close().
(3) The ZipFileInputStream methods read(byte,int,int) and read()
return -1 after ZipFile.close() has been called.
(4) ZipFile.close() should be synchronized in case one of the read
methods is called from another thread.
A suggested fix is supplied.