Fix NPE

[Koyorice]

Fixes NPE that occurs when both save-empty-inventories and allow-other-plugins-edit-death-inventory are set to false and a player dies with an empty inventory

To avoid NPE in ConcurrentHashMap we can't simply add null check for snapshot. Doing so would cause playerDeathHandle to skip pre-death validation when inventories are empty

This change replaces null returns with a static empty snapshot, allow deathPreSnapshots to safely store the state while ensuring that empty inventories are correctly ignored across all saving logic without NPE

EventLogs.java#L126

NPE stacktrace

[23:17:48 ERROR]: Could not pass event EntityDamageEvent to InventoryRollbackPlus v1.8.0
java.lang.NullPointerException
        at java.base/java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1023) ~[?:?]
        at java.base/java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:1018) ~[?:?]
        at InventoryRollbackPlus-1.8.0.jar//me.danjono.inventoryrollback.listeners.EventLogs.playerPreDeath(EventLogs.java:126) ~[?:?]
        at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:80) ~[paper-api-1.21.11-R0.1-SNAPSHOT.jar:?]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:71) ~[paper-api-1.21.11-R0.1-SNAPSHOT.jar:?]
        at io.papermc.paper.plugin.manager.PaperEventManager.callEvent(PaperEventManager.java:54) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at io.papermc.paper.plugin.manager.PaperPluginManagerImpl.callEvent(PaperPluginManagerImpl.java:131) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:628) ~[paper-api-1.21.11-R0.1-SNAPSHOT.jar:?]
        at org.bukkit.event.Event.callEvent(Event.java:46) ~[paper-api-1.21.11-R0.1-SNAPSHOT.jar:?]
        at org.bukkit.craftbukkit.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:1190) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at org.bukkit.craftbukkit.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:1180) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at org.bukkit.craftbukkit.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:1170) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at org.bukkit.craftbukkit.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:1071) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at org.bukkit.craftbukkit.event.CraftEventFactory.handleLivingEntityDamageEvent(CraftEventFactory.java:1234) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.entity.LivingEntity.handleEntityDamage(LivingEntity.java:2441) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.entity.LivingEntity.hurtServer(LivingEntity.java:1486) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.entity.player.Player.hurtServer(Player.java:756) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.server.level.ServerPlayer.hurtServer(ServerPlayer.java:1300) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.entity.LivingEntity.causeFallDamage(LivingEntity.java:2242) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.entity.player.Player.causeFallDamage(Player.java:1557) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.level.block.Block.fallOn(Block.java:523) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.entity.Entity.checkFallDamage(Entity.java:1947) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.entity.LivingEntity.checkFallDamage(LivingEntity.java:409) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.server.level.ServerPlayer.checkFallDamage(ServerPlayer.java:1767) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.world.entity.Entity.doCheckFallDamage(Entity.java:1936) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.server.network.ServerGamePacketListenerImpl.handleMovePlayer(ServerGamePacketListenerImpl.java:1712) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.network.protocol.game.ServerboundMovePlayerPacket.handle(ServerboundMovePlayerPacket.java:62) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.network.protocol.game.ServerboundMovePlayerPacket$PosRot.handle(ServerboundMovePlayerPacket.java:137) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.network.PacketProcessor$ListenerAndPacket.handle(PacketProcessor.java:99) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.network.PacketProcessor.executeSinglePacket(PacketProcessor.java:33) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1504) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.server.MinecraftServer.recordTaskExecutionTimeWhileWaiting(MinecraftServer.java:1230) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1346) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:388) ~[paper-1.21.11.jar:1.21.11-113-6103cc7]
        at java.base/java.lang.Thread.run(Thread.java:1474) ~[?:?]