MDEV-20934: Correct a debug assertion

A search with PAGE_CUR_GE may land on the supremum record on
a leaf page that is not the rightmost leaf page.
This could occur when all keys on the current page are
smaller than the search key, and the smallest key on the
successor page is larger than the search key.

ibuf_delete_recs(): Correct the debug assertion accordingly.

storage/innobase/ibuf/ibuf0ibuf.cc

@@ -4349,7 +4349,7 @@ ATTRIBUTE_COLD static void ibuf_delete_recs(const page_id_t page_id)
 		      &pcur, &mtr);
 
 	if (!btr_pcur_is_on_user_rec(&pcur)) {
-		ut_ad(btr_pcur_is_after_last_in_tree(&pcur, &mtr));
+		ut_ad(btr_pcur_is_after_last_on_page(&pcur));
 		goto func_exit;
 	}