btr_cur_optimistic_delete_func(): Remove the record lock also when the page becomes empty

btr_cur_pessimistic_delete(): Remove the record lock also when the
page is dropped. FIXME: File a bug for this and fix in 5.5+. The bug
is present in all InnoDB versions.

storage/innobase/btr/btr0cur.cc

@@ -5211,6 +5211,7 @@ btr_cur_optimistic_delete_func(
 			      page_rec_get_next_const(
 				      page_get_infimum_rec(block->frame)),
 			      index));
+		lock_update_delete(block, btr_cur_get_rec(cursor));
 		btr_page_empty(block, buf_block_get_page_zip(block),
 			       index, 0, mtr);
 		page_cur_set_after_last(block, btr_cur_get_page_cur(cursor));
@@ -5386,6 +5387,10 @@ btr_cur_pessimistic_delete(
 #endif /* UNIV_ZIP_DEBUG */
 	}
 
+	if (flags == 0) {
+		lock_update_delete(block, rec);
+	}
+
 	if (UNIV_UNLIKELY(page_get_n_recs(page) < 2)
 	    && UNIV_UNLIKELY(dict_index_get_page(index)
 			     != block->page.id.page_no())) {
@@ -5400,10 +5405,6 @@ btr_cur_pessimistic_delete(
 		goto return_after_reservations;
 	}
 
-	if (flags == 0) {
-		lock_update_delete(block, rec);
-	}
-
 	if (page_is_leaf(page)) {
 		if (UNIV_UNLIKELY(page_is_root(page)
 				  && page_get_n_recs(page)