btr_cur_optimistic_insert(): Remove a bogus assertion. The insert may
fail after reorganizing the page.

btr_cur_optimistic_update(): Do not attempt to reorganize compressed pages,
because compression may fail after reorganization.

page_copy_rec_list_start(): Use page_rec_get_nth() to restore to the
ret_pos, which may also be the page infimum.

rb:1221