windowscodecs: pceltFetched is optional in IWICEnumMetadataItem.

dlls/windowscodecs/metadatahandler.c

@@ -491,9 +491,13 @@ static HRESULT WINAPI MetadataHandlerEnum_Next(IWICEnumMetadataItem *iface,
     ULONG new_index;
     HRESULT hr=S_FALSE;
     ULONG i;
+    ULONG fetched;
 
     TRACE("(%p,%li)\n", iface, celt);
 
+    if (!pceltFetched)
+        pceltFetched = &fetched;
+
     EnterCriticalSection(&This->parent->lock);
 
     if (This->index >= This->parent->item_count)

dlls/windowscodecs/tests/metadata.c

@@ -303,6 +303,21 @@ static void test_metadata_unknown(void)
         ok(hr == S_FALSE, "Next failed, hr=%lx\n", hr);
         ok(items_returned == 0, "unexpected item count %li\n", items_returned);
 
+        hr = IWICEnumMetadataItem_Reset(enumerator);
+        ok(hr == S_OK, "Reset failed, hr=%lx\n", hr);
+
+        hr = IWICEnumMetadataItem_Next(enumerator, 1, &schema, &id, NULL, NULL);
+        ok(hr == S_OK, "Next failed, hr=%lx\n", hr);
+
+        if (hr == S_OK)
+        {
+            ok(schema.vt == VT_EMPTY, "unexpected vt: %i\n", schema.vt);
+            ok(id.vt == VT_EMPTY, "unexpected vt: %i\n", id.vt);
+
+            PropVariantClear(&schema);
+            PropVariantClear(&id);
+        }
+
         IWICEnumMetadataItem_Release(enumerator);
     }