A misplaced btr_cur_need_opposite_intention() check may fail to prevent hangs

In MDEV-30400 the function btr_cur_t::search_leaf() replaced the function btr_cur_search_to_nth_level() for the case level=0. That code was revised in MDEV-29385 with regard to the function btr_cur_need_opposite_intention().

Upon reaching the leaf level, one call to btr_cur_need_opposite_intention() is misplaced. Before these changes, btr_cur_search_to_nth_level() would invoke btr_cur_need_opposite_intention() after positioning page_cur_t::rec on the current page. As a result of the misplaced call, the calls to page_rec_is_last() and page_rec_is_first() would never seem to hold, because the page and rec would be within different buffer pool blocks.

The purpose of the function btr_cur_need_opposite_intention() is to detect when a page split could occur. As far as I can tell, this bug could cause a hang similar to the ones that the fix of MDEV-29835 attempted to address. Possibly, this bug could explain MDEV-31815.