Fix screen resolution bigger than map resolution bug

[KevinHake]

For small maps and modern (e.g. 4k) screens, TA doesn't handle things well - the original code assumed the map always contains more vertical and horizontal length than the screen.

Background/existing behavior: All maps have a zone around the edge that was never intended to be drawn, or have user commands in them, but it helps avoid units getting stuck on edges while turning around etc (people use this to their advantage with planes). With a large screen and small map, that edge region may render, and if the game doesn't crash, scrolling can be sporadic, rapidly drawing the map first on the left, then the right, with screen poop in the remaining extra area (I've seen this on The Desert Triad and a 4k monitor).

Required behavior:

• Only render the map inside the outer "dead zone"
• Never allow user commands to be given in the "dead zone" or beyond (not sure if this is actually possible/an issue)
• Ensure moving the mouse to the edge still scrolls if the map is bigger than the screen in that (x or y) direction (and doesn't do anything when it's the same size or smaller)

In the case a map is smaller than the display (minus size of menus), it's probably ideal to draw the map immediately adjacent to the menus/info bar, just from a UI perspective (put info/buttons as close to the action as possible). That might already be the default behavior. Probably fine to fill the extra space with black pixels (that's what the game draws under the menu when resolution is large already). Would be cool to fill extra space with a texture matching the rest of the UI, and for the case where there is extra vertical space, move the bottom info bar up to the bottom edge of the map (with empty texture underneath).

[KevinHake]

You'd want to test behavior for the following: both x/y size of the map < screen x/y: the normal case (regression test; we don't want to break that) both x/y of the map > screen x/y only x > screen x only y > screen y