Fix various map generator bounds and size related issues

- If generating a RectangularIsometric map via lobby, make the height
  twice the width so that the map is approximately world-square.
- Use equal top and bottom cordons for RectangularIsometric maps.
- Change some map bounds checking.
- Check that actors are at least partially inside map.Contains before
  placing. (To avoid frozen actor crashes.)
- Fix editor generated map blitting for RectangularIsometric.

OpenRA.Mods.Common/Widgets/Logic/MapGeneratorLogic.cs

@@ -234,9 +234,15 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 
 		void RandomizeSize()
 		{
+			var mapGrid = modData.Manifest.Get<MapGrid>();
 			var sizeRange = MapSizes[selectedSize];
 			var width = Game.CosmeticRandom.Next(sizeRange.X, sizeRange.Y);
-			size = new Size(width + 2, width + 2);
+			var height =
+				mapGrid.Type == MapGridType.RectangularIsometric
+					? width * 2
+					: width;
+
+			size = new Size(width + 2, height + mapGrid.MaximumTerrainHeight * 2 + 2);
 		}
 
 		void RefreshSettings()