tile animation: synthesize ANIMBIT when saving (for compatibility)

Also, add some safety checks in case Tiles.get() is called with an out-of-range tile number.

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@739 d9718cc8-9f43-0410-858b-315f434eb58c

src/micropolisj/engine/Tiles.java

@@ -50,6 +50,11 @@ public class Tiles
 
 	public static TileSpec get(int tileNumber)
 	{
-		return tiles[tileNumber];
+		if (tileNumber >= 0 && tileNumber < tiles.length) {
+			return tiles[tileNumber];
+		}
+		else {
+			return null;
+		}
 	}
 }