The modification is based on a preallocation space in the Extra field using a phony custom block in the Local file header. This space is eventually overwritten by the ZIP64 extension if the file exceeds 4GiB.
Also were fixed differences from PKZip specification in the streaming interface.
mz_zip_writer_add_staged_open(), mz_zip_writer_add_staged_data() and mz_zip_writer_add_staged_finish()
were derived from mz_zip_writer_add_read_buf_callback() by splitting it and passing a new
mz_zip_writer_staged_context between them.
