GLK ZCODE: Shogun fails to launch

[dfabulich]

Shogun is a Z6 game. When you launch it, ScummVM prints a warning, "The game you are about to start is not yet fully supported by ScummVM."

One of the weird things about Z6 games is that they include graphics, but the graphics are not distributed directly inside the Z6. Instead, Frotz launches the game with two files: the Z6, and a corresponding "Blorb" file that contains the graphics.

IFWiki has documentation on how to download and run Shogun with Frotz; it works fine there. ​https://www.ifwiki.org/Shogun

To repro:

1. Create a directory containing shogun-r322-s890706.z6 and shogun-r322-s890706.blb (following the instructions from the IFWiki)
2. Add that directory to ScummVM. ScummVM will recognize the game as "James Clavell's Shogun"
3. Launch the game, click "Start anyway" at the error page
4. You'll see the launch screen, "SHOGUN". Press any key.

Actual: The next screen says, "You may choose to" and nothing else.

Expected: It should display the graphics correctly, and ask whether you want to start the game, restore, or quit, with graphic tiles on the left and right of the menu.