Gen 1-2: Fix TOX -> PSN display

Because the TOX -> PSN change happened onSwitchIn, it wouldn't display
correctly on the first switch after TOX, requiring two switches to
display correctly.

This corrects the change to onBeforeSwitchIn, where it will display
correctly for the first switch.

data/mods/gen2/statuses.js

@@ -113,7 +113,7 @@ let BattleStatuses = {
 		onAfterMoveSelf(pokemon) {
 			this.damage(this.clampIntRange(Math.floor(pokemon.maxhp / 16), 1) * pokemon.volatiles['residualdmg'].counter, pokemon, pokemon);
 		},
-		onSwitchIn(pokemon) {
+		onBeforeSwitchIn(pokemon) {
 			// Regular poison status and damage after a switchout -> switchin.
 			pokemon.status = /** @type {ID} */('psn');
 		},