将DEFAULT_ICON移至Constants, 并使用懒加载

当类初始化时, JavaFX可能还未启动, 这将使图像加载失败

HMCLCore/src/main/java/org/jackhuang/hmcl/util/Constants.java

@@ -19,6 +19,11 @@ package org.jackhuang.hmcl.util;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+
+import javafx.beans.binding.Bindings;
+import javafx.beans.binding.ObjectBinding;
+import javafx.scene.image.Image;
+
 import org.jackhuang.hmcl.game.Argument;
 import org.jackhuang.hmcl.game.Library;
 import org.jackhuang.hmcl.game.RuledArgument;
@@ -65,6 +70,9 @@ public final class Constants {
             javafx.application.Platform.runLater(s);
     };
 
+    // lazy loading
+    public static final ObjectBinding<Image> DEFAULT_ICON = Bindings.createObjectBinding(() -> new Image("/assets/img/icon.png"));
+
     public static final Gson GSON = new GsonBuilder()
             .enableComplexMapKeySerialization()
             .setPrettyPrinting()