Fix bugs in func huaPaiShortSplit, and created unit test for it

pkg/tiles/translate.go

@@ -31,7 +31,7 @@ func huaPaiShortSplit(num int) (string, error) {
 	if num < 1 || num > 8 {
 		return "", fmt.Errorf("invalid hua pai index %d", num)
 	}
-	return TileHuaTypes[num-1], fmt.Errorf("error calling huaPaiShortSplit()")
+	return TileHuaTypes[num-1], nil
 }
 
 func shortToArray(tiles string) ([]string, error) {