RemoteImageLoader 在图标尚未加载时应当将图像更新为占位符 (#5239)

HMCL/src/main/java/org/jackhuang/hmcl/util/RemoteImageLoader.java

@@ -66,6 +66,8 @@ public abstract class RemoteImageLoader {
             cache.remove(uri);
         }
 
+        writableValue.setValue(getPlaceholder());
+
         {
             List<WeakReference<WritableValue<Image>>> list = pendingRequests.get(uri);
             if (list != null) {