Fix panic on async io due to reading locked page

core/storage/btree.rs

@@ -1944,6 +1944,7 @@ impl BTreeCursor {
                 let current_sibling = sibling_pointer;
                 for i in (0..=current_sibling).rev() {
                     let page = self.pager.read_page(pgno as usize)?;
+                    return_if_locked!(page);
                     debug_validate_cells!(&page.get_contents(), self.usable_space() as u16);
                     pages_to_balance[i].replace(page);
                     assert_eq!(