MDEV-25979 Invalid page number written to DB_ROLL_PTR

trx_undo_report_row_operation(): Fix a race condition that was introduced
in commit f74023b9 (MDEV-15090).
We must not access undo_block after the page latch has been released
in mtr_t::commit(), because the block could be evicted or replaced.

storage/innobase/trx/trx0rec.cc

@@ -2054,12 +2054,11 @@ trx_undo_report_row_operation(
 				goto err_exit;
 			}
 
-			mtr_commit(&mtr);
+			mtr.commit();
 		} else {
 			/* Success */
-			mtr_commit(&mtr);
-
 			undo->top_page_no = undo_block->page.id.page_no();
+			mtr.commit();
 			undo->top_offset  = offset;
 			undo->top_undo_no = trx->undo_no++;
 			undo->guess_block = undo_block;