Fix Baton Pass breaking on Memento (#4773)

* Fix Baton Pass breaking on Memento

* doubled headers

src/battle_script_commands.c

@@ -7032,8 +7032,12 @@ static void Cmd_openpartyscreen(void)
                 if (gAbsentBattlerFlags & gBitTable[battlerOpposite])
                     battlerOpposite ^= BIT_FLANK;
 
-                BtlController_EmitLinkStandbyMsg(battlerOpposite, BUFFER_A, LINK_STANDBY_MSG_ONLY, FALSE);
-                MarkBattlerForControllerExec(battlerOpposite);
+                // Make sure we're checking a valid battler. In edge case scenarios - battler could be absent and battlerOpposite would become a non-existent one softlocking the game.
+                if (battlerOpposite < gBattlersCount)
+                {
+                    BtlController_EmitLinkStandbyMsg(battlerOpposite, BUFFER_A, LINK_STANDBY_MSG_ONLY, FALSE);
+                    MarkBattlerForControllerExec(battlerOpposite);
+                }
             }
         }
     }

test/battle/move_effect/baton_pass.c

@@ -1,6 +1,30 @@
 #include "global.h"
 #include "test/battle.h"
 
+ASSUMPTIONS
+{
+    ASSUME(gMovesInfo[MOVE_BATON_PASS].effect == EFFECT_BATON_PASS);
+}
+
+// This softlocked the game before.
+SINGLE_BATTLE_TEST("Baton Pass used after Memento works correctly")
+{
+    GIVEN {
+        PLAYER(SPECIES_WOBBUFFET);
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_WYNAUT);
+        OPPONENT(SPECIES_CATERPIE);
+    } WHEN {
+        TURN { MOVE(player, MOVE_MEMENTO); SEND_OUT(player, 1); MOVE(opponent, MOVE_BATON_PASS); SEND_OUT(opponent, 1); }
+    } SCENE {
+        MESSAGE("Wobbuffet used Memento!");
+        MESSAGE("Wobbuffet fainted!");
+        MESSAGE("Foe Wynaut used Baton Pass!");
+        MESSAGE("2 sent out Caterpie!");
+        MESSAGE("Go! Wobbuffet!");
+    }
+}
+
 TO_DO_BATTLE_TEST("Baton Pass switches out the user");
 TO_DO_BATTLE_TEST("Baton Pass fails if there's no valid party Pokémon left");
 TO_DO_BATTLE_TEST("Baton Pass passes both positive and negative stat changes");