Ensure we actually removed entity from chunk before decrementing counts

If a plugin hacks into NMS and triggers entity removal, it could
result in an entity being attempted to remove from the chunk twice.

The 2nd pass will return false, as it did not find the entity in the list.

We should not touch entity counts if the entity was not removed, to avoid
going negative.

Spigot-Server-Patches/Fix-Bugs-with-Spigot-Mob-Spawn-Logic.patch

@@ -13,6 +13,19 @@ Specially with servers using smaller mob spawn ranges than view distance, as wel
 
 This patch returns mob counting to use all loaded chunks, and 17x17 division.
 
+diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/net/minecraft/server/Chunk.java
++++ b/src/main/java/net/minecraft/server/Chunk.java
+@@ -0,0 +0,0 @@ public class Chunk {
+             i = this.entitySlices.length - 1;
+         }
+ 
+-        this.entitySlices[i].remove(entity);
++        if (!this.entitySlices[i].remove(entity)) { return; } // Paper
+         // Paper start - update counts
+         if (entity instanceof EntityItem) {
+             itemCounts[i]--;
 diff --git a/src/main/java/net/minecraft/server/SpawnerCreature.java b/src/main/java/net/minecraft/server/SpawnerCreature.java
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
 --- a/src/main/java/net/minecraft/server/SpawnerCreature.java

Spigot-Server-Patches/MC-Utils.patch

@@ -120,6 +120,10 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        return new Location(entity.getWorld().getWorld(), entity.locX, entity.locY, entity.locZ);
 +    }
 +
++    public static BlockPosition toBlockPosition(Location loc) {
++        return new BlockPosition(loc.getBlockX(), loc.getBlockY(), loc.getBlockZ());
++    }
++
 +    public static boolean isEdgeOfChunk(BlockPosition pos) {
 +        final int modX = pos.getX() & 15;
 +        final int modZ = pos.getZ() & 15;