Changed to allow unpacking in memory

[Idanlu]

[pmachapman]

Hi, I won't merge your pull request as this is just a mirror of the unrar source code from rarlab.com.

I will however leave your pull request open for now, as your change may interest people building their own unrar exe or dll.

NOTE: I am not affiliated with win.rar GmbH in any way - I have put these files up on GitHub as a convenience.