A drug-addicted Long Island mom allegedly fed her 18-month old son unpopped popcorn kernels in a drunken stupor — then left him and her other child alone so she could drink in the bathroom while the toddler was choking to death. Olivia Bithorn, 36, was busted after Nassau County cops were called to her Merrick home, where they found Bithron’s son, Luke Russell Jr., laying on the ground surrounded by popcorn kernels and turning blue — just steps away from an empty bottle of Tito’s vodka in the