Only assign blockstate data if super ctor did not (#10841)

The CraftBlockStateMeta constructor CraftBlockStateMeta(Map) invokes its
parent constructor, which itself invokes deserializeInternal, which is
implemented on CraftBlockStateMeta to read the components and block
entity tag from the passed map.

Field initialization happens after the call to the super constructor,
meaning the current code overwrites the parsed internal data with the
EMPTY defaults.

This is prevented by moving the initialization into its own code block
that can null check the fields prior to defaulting their value to EMPTY.

patches/server/General-ItemMeta-fixes.patch

@@ -168,8 +168,15 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      final Material material;
 -    private CraftBlockEntityState<?> blockEntityTag;
 +    // Paper start - store data separately
-+    DataComponentMap components = DataComponentMap.EMPTY;
-+    CustomData blockEntityTag = CustomData.EMPTY;
++    DataComponentMap components;
++    CustomData blockEntityTag;
++    {
++        // this is because the fields are possibly assigned in the super constructor (via deserializeInternal)
++        // and a direct field initialization happens **after** the super constructor. So we only want to
++        // set them to empty if they weren't assigned by the super constructor (via deserializeInternal)
++        this.components = this.components != null ? this.components : DataComponentMap.EMPTY;
++        this.blockEntityTag = this.blockEntityTag != null ? this.blockEntityTag : CustomData.EMPTY;
++    }
 +    private Material materialForBlockEntityType() {
 +        return (this.material != Material.SHIELD) ? this.material : CraftMetaBlockState.shieldToBannerHack();
 +    }
@@ -300,10 +307,10 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        // Paper start - new serialization format
 +        if (tag.contains(CraftMetaBlockState.BLOCK_ENTITY_TAG_CUSTOM_DATA.NBT, CraftMagicNumbers.NBT.TAG_COMPOUND)) {
 +            this.blockEntityTag = CustomData.of(tag.getCompound(CraftMetaBlockState.BLOCK_ENTITY_TAG_CUSTOM_DATA.NBT));
-+        }
+         }
 +        if (tag.contains(CraftMetaBlockState.BLOCK_ENTITY_COMPONENTS.NBT, CraftMagicNumbers.NBT.TAG_COMPOUND)) {
 +            this.components = DataComponentMap.CODEC.parse(org.bukkit.craftbukkit.CraftRegistry.getMinecraftRegistry().createSerializationContext(net.minecraft.nbt.NbtOps.INSTANCE), tag.getCompound(CraftMetaBlockState.BLOCK_ENTITY_COMPONENTS.NBT)).getOrThrow();
-         }
++        }
 +        // Paper end - new serialization format
      }
  
@@ -314,11 +321,11 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        // Paper start - new serialization format
 +        if (!this.blockEntityTag.isEmpty()) {
 +            internalTags.put(CraftMetaBlockState.BLOCK_ENTITY_TAG_CUSTOM_DATA.NBT, this.blockEntityTag.getUnsafe()); // unsafe because it's serialized right away
-         }
++        }
 +        if (!this.components.isEmpty()) {
 +            final Tag componentsTag = DataComponentMap.CODEC.encodeStart(org.bukkit.craftbukkit.CraftRegistry.getMinecraftRegistry().createSerializationContext(net.minecraft.nbt.NbtOps.INSTANCE), this.components).getOrThrow();
 +            internalTags.put(CraftMetaBlockState.BLOCK_ENTITY_COMPONENTS.NBT, componentsTag);
-+        }
+         }
 +        // Paper end - new serialization format
      }