Check pending blocks before falling back to world. Fixes BUKKIT-5122

When growing trees we use a BlockChangeDelegate which queues up the block
changes so plugins can modify/block/log tree growing. However, we always
check the actual world when checking for existing blocks. This means when
the tree growing code checks to see if putting a leaf in a block is valid
it may incorrectly overwrite a log block that should exist in that
location. To ensure trees grow correctly we now check the delegate itself
for blocks that match the queried location before checking the world.

src/main/java/org/bukkit/craftbukkit/util/StructureGrowDelegate.java

@@ -3,6 +3,8 @@ package org.bukkit.craftbukkit.util;
 import java.util.ArrayList;
 import java.util.List;
 
+import net.minecraft.server.Block;
+import net.minecraft.server.Blocks;
 import net.minecraft.server.World;
 
 import org.bukkit.BlockChangeDelegate;
@@ -39,6 +41,12 @@ public class StructureGrowDelegate implements BlockChangeDelegate {
     }
 
     public int getTypeId(int x, int y, int z) {
+        for (BlockState state : blocks) {
+            if (state.getX() == x && state.getY() == y && state.getZ() == z) {
+                return state.getTypeId();
+            }
+        }
+
         return world.getBlockTypeIdAt(x, y, z);
     }
 
@@ -51,6 +59,12 @@ public class StructureGrowDelegate implements BlockChangeDelegate {
     }
 
     public boolean isEmpty(int x, int y, int z) {
+        for (BlockState state : blocks) {
+            if (state.getX() == x && state.getY() == y && state.getZ() == z) {
+                return Block.e(state.getTypeId()) == Blocks.AIR;
+            }
+        }
+
         return world.getBlockAt(x, y, z).isEmpty();
     }
 }