Unexpected screen size can crash Infocom V6 games

[DFillmore]

The V6 Infocom games expect a screen size of 320/200. If the ratio does not match this, Zork Zero will place various screen elements (right border image, compass direction images) in the wrong place, and sometimes even crash.

A possible fix for this, to allow the application window to be resized without breaking the game, would be to check if the game is one of these four, and fix the 'Z-Machine screen' at the correct ratio, and center it with empty borders at left/right or top/bottom if Viola's window is the wrong size.

[DFillmore]

Marked as enhancement rather than bug because technically the V6 games are making incorrect assumptions about screen size and doing weird stuff if they're wrong.