unattended-file: Handle 'floppy' injection method

This script injection method was forgotten when we added handling of
injection methods and it broke express installation for windows.
downloader: Handle downloads of unknown size

Currently if size of file being downloaded is unknown, we download the
bytes but just ignore the bytes. This patch fixes this case by writing
the downloaded bytes to the file but just not reporting progress if size
is unknown.
Release 3.14.1.1