Move initial map suitability calculation to MapCache.

This was previously trying to use values that had
not yet been initialised, which meant that *all*
maps were treated as unsuitable.  This would cause
the mod to always fall back to the first installed
map.

OpenRA.Game/Map/MapCache.cs

@@ -243,11 +243,31 @@ namespace OpenRA
 				});
 		}
 
+		bool IsSuitableInitialMap(MapPreview map)
+		{
+			if (map.Status != MapStatus.Available || !map.Visibility.HasFlag(MapVisibility.Lobby))
+				return false;
+
+			// Other map types may have confusing settings or gameplay
+			if (!map.Categories.Contains("Conquest"))
+				return false;
+
+			// Maps with bots disabled confuse new players
+			if (map.Players.Players.Any(x => !x.Value.AllowBots))
+				return false;
+
+			// Large maps expose unfortunate performance problems
+			if (map.Bounds.Width > 128 || map.Bounds.Height > 128)
+				return false;
+
+			return true;
+		}
+
 		public string ChooseInitialMap(string initialUid, MersenneTwister random)
 		{
 			if (string.IsNullOrEmpty(initialUid) || previews[initialUid].Status != MapStatus.Available)
 			{
-				var selected = previews.Values.Where(x => x.SuitableForInitialMap).RandomOrDefault(random) ??
+				var selected = previews.Values.Where(IsSuitableInitialMap).RandomOrDefault(random) ??
 					previews.Values.First(m => m.Status == MapStatus.Available && m.Visibility.HasFlag(MapVisibility.Lobby));
 				return selected.Uid;
 			}