[Bleeding] Ignore Block Physics in Chunk population. Fixes BUKKIT-4923

Suppressing physics updates during Chunk population prevents
infinite recursion due to custom Block Populators editing border
blocks on chunks.

src/main/java/net/minecraft/server/ChunkProviderServer.java

@@ -237,8 +237,13 @@ public class ChunkProviderServer implements IChunkProvider {
 
                 org.bukkit.World world = this.world.getWorld();
                 if (world != null) {
-                    for (org.bukkit.generator.BlockPopulator populator : world.getPopulators()) {
-                        populator.populate(world, random, chunk.bukkitChunk);
+                    this.world.populating = true;
+                    try {
+                        for (org.bukkit.generator.BlockPopulator populator : world.getPopulators()) {
+                            populator.populate(world, random, chunk.bukkitChunk);
+                        }
+                    } finally {
+                        this.world.populating = false;
                     }
                 }
                 BlockSand.instaFall = false;

src/main/java/net/minecraft/server/World.java

@@ -70,6 +70,7 @@ public abstract class World implements IBlockAccess {
     public boolean callingPlaceEvent = false;
     public long ticksPerAnimalSpawns;
     public long ticksPerMonsterSpawns;
+    public boolean populating;
     // CraftBukkit end
     private ArrayList M;
     private boolean N;
@@ -398,6 +399,11 @@ public abstract class World implements IBlockAccess {
     }
 
     public void update(int i, int j, int k, Block block) {
+        // CraftBukkit start
+        if (this.populating) {
+            return;
+        }
+        // CraftBukkit end
         this.applyPhysics(i, j, k, block);
     }