Fixed advancement background texture not shown due to invalid path parsing (#2744)

Author: Neocky

v1_21/src/main/java/com/denizenscript/denizen/nms/v1_21/helpers/AdvancementHelperImpl.java

@@ -147,9 +147,15 @@ private static AdvancementHolder asNMSCopy(com.denizenscript.denizen.nms.util.Ad
         AdvancementHolder parent = advancement.parent != null
                 ? getNMSAdvancementManager().advancements.get(CraftNamespacedKey.toMinecraft(advancement.parent))
                 : null;
+        ClientAsset clientAsset = Optional.ofNullable(advancement.background).map(Object::toString).map(ResourceLocation::parse)
+                .filter(rl -> rl.getPath().startsWith("textures/") && rl.getPath().endsWith(".png"))
+                .map(rl -> new ClientAsset(
+                        rl.withPath(p -> p.substring("textures/".length(), p.length() - ".png".length())),
+                        rl))
+                .orElse(null); // converts the background into a ClientAsset if it's a valid png texture path under "textures/", otherwise returns null
         DisplayInfo display = new DisplayInfo(CraftItemStack.asNMSCopy(advancement.icon),
                 Handler.componentToNMS(FormattedTextHelper.parse(advancement.title, ChatColor.WHITE)), Handler.componentToNMS(FormattedTextHelper.parse(advancement.description, ChatColor.WHITE)),
-                Optional.ofNullable(advancement.background).map(CraftNamespacedKey::toMinecraft).map(ClientAsset::new), AdvancementType.valueOf(advancement.frame.name()),
+                Optional.ofNullable(clientAsset), AdvancementType.valueOf(advancement.frame.name()),
                 advancement.toast, advancement.announceToChat, advancement.hidden);
         display.setLocation(advancement.xOffset, advancement.yOffset);
         Map<String, Criterion<?>> criteria = IMPOSSIBLE_CRITERIA;