调整卡牌攻击

- 场上存在卡牌时无法直接攻击敌方玩家
- 取消卡牌攻击敌方玩家高亮显示
- 一回合只能上场一张角色卡

Assets/TcgEngine/Scripts/UI/IconBar.cs

@@ -33,9 +33,15 @@ namespace TcgEngine.UI
 
         public void Refresh()
         {
+            if (icons == null)
+                return;
+                
             int index = 0;
             foreach (Image icon in icons)
             {
+                if (icon == null)
+                    continue;
+                    
                 icon.gameObject.SetActive(index < value || index < max_value);
                 icon.sprite = (index < value) ? sprite_full : sprite_empty;
                 index++;
@@ -44,9 +50,13 @@ namespace TcgEngine.UI
 
         public void SetMat(Material mat)
         {
+            if (icons == null)
+                return;
+                
             foreach (Image icon in icons)
             {
-                icon.material = mat;
+                if (icon != null)
+                    icon.material = mat;
             }
         }
     }