Windows cf-upgrade self-exec fix.

The following "add a space" only happens if `args[0]` is non-empty (which it probably is, but I'm paranoid).
So the later "roll back" should be conditioned on `i > 0`.
Obviously, our caller had better have allocated `command_line` to be big enough for sum(strlen(args[i]), i from 0 while args[i] isn't NULL) bytes.