Fix the issue on the web platform where attachmentVertices fails to retrieve properly after the attachment is set by another skeletonData. (#18890)

Author: bofeng-song

native/cocos/editor-support/spine-wasm/spine-skeleton-instance.cpp

@@ -294,6 +294,9 @@ void SpineSkeletonInstance::collectMeshData() {
         AttachmentVertices *attachmentVertices = nullptr;
         if (attachmentVerticesMap->containsKey(attachmentSlot)) {
             attachmentVertices = (*attachmentVerticesMap)[attachmentSlot];
+        } else {
+            // attachment set from other skeletonData
+            attachmentVertices = getAttachmentVertices(attachmentSlot);
         }
         if (_userData.useSlotTexture && _slotTextureSet.containsKey(slot)) {
             auto info = _slotTextureSet[slot];

native/external-config.json

@@ -3,6 +3,6 @@
         "type": "github",
         "owner": "cocos",
         "name": "cocos-engine-external",
-        "checkout": "v3.8.7-17"
+        "checkout": "v3.8.7-18"
     }
 }