value of the block that the cursor points to.

row_ins_check_foreign_constraint(): Call btr_pcur_get_block() after
row_ins_foreign_check_on_constraint(), as it may reposition the cursor
on a different page.

row_ins_scan_sec_index_for_duplicate(): Call btr_pcur_get_block() on
every iteration of the loop.  Use do ... while instead of for (;;).