MDEV-22773 Assertion page_get_page_no... in btr_pcur_store_position()

btr_pcur_store_position(): Replace a too strict debug assertion.
It is possible to have a clustered index B-tree for a logically
empty table, which will consist of a node pointer from the root
page to a leaf page that contains the metadata record.

The too strict debug assertion was added in
commit 0e5a4ac2 (MDEV-15562).

storage/innobase/btr/btr0pcur.cc

@@ -154,7 +154,7 @@ btr_pcur_store_position(
 			ut_ad(index->table->instant);
 			ut_ad(page_get_n_recs(block->frame) == 1);
 			ut_ad(page_is_leaf(block->frame));
-			ut_ad(page_get_page_no(block->frame) == index->page);
+			ut_ad(!page_has_siblings(block->frame));
 			cursor->rel_pos = BTR_PCUR_AFTER_LAST_IN_TREE;
 			return;
 		}