Fix NPE when completing skull lookups without a real owner (Fixes #6052)

This looks like mojang introduced an NPE however it was previously being
supressed by the future used by the server, we'll just stick to the legacy
behavior of retainining the existing profile of earlier versions

patches/server/0723-Don-t-complete-skull-lookups-on-main-thread-MC-22743.patch

@@ -5,16 +5,20 @@ Subject: [PATCH] Don't complete skull lookups on main thread (MC-227435)
 
 
 diff --git a/src/main/java/net/minecraft/world/level/block/entity/SkullBlockEntity.java b/src/main/java/net/minecraft/world/level/block/entity/SkullBlockEntity.java
-index 172413fc0f303d5e15bc2bc55c09ce4faf5298a0..705d5ebb3d7b40745b318617ea39a7ea785b9504 100644
+index 172413fc0f303d5e15bc2bc55c09ce4faf5298a0..96863338e1642105f71e681ec2b32c882b3ea342 100644
 --- a/src/main/java/net/minecraft/world/level/block/entity/SkullBlockEntity.java
 +++ b/src/main/java/net/minecraft/world/level/block/entity/SkullBlockEntity.java
-@@ -145,15 +145,24 @@ public class SkullBlockEntity extends BlockEntity {
+@@ -145,15 +145,28 @@ public class SkullBlockEntity extends BlockEntity {
  
      public static void updateGameprofile(@Nullable GameProfile owner, Consumer<GameProfile> callback) {
          if (owner != null && !StringUtil.isNullOrEmpty(owner.getName()) && (!owner.isComplete() || !owner.getProperties().containsKey("textures")) && SkullBlockEntity.profileCache != null && SkullBlockEntity.sessionService != null) {
 -            SkullBlockEntity.profileCache.getAsync(owner.getName(), (gameprofile1) -> {
 +            // Paper start
 +            SkullBlockEntity.profileCache.getAsync(owner.getName(), (gameprofile) -> {
++                if (gameprofile == null) {
++                    net.minecraft.server.MinecraftServer.getServer().scheduleOnMain(() -> callback.accept(owner));
++                    return;
++                }
 +                Runnable runnable = () -> {
 +                GameProfile gameprofile1 = gameprofile;
                  Property property = (Property) Iterables.getFirst(gameprofile1.getProperties().get("textures"), (Object) null);