SPIGOT-4591: Must mark itemstacks as dirty in case the handle itself changed

nms-patches/EntityItem.patch

@@ -120,11 +120,13 @@
              if (this.pickupDelay == 0 && (this.g == null || 6000 - this.age <= 200 || this.g.equals(entityhuman.getUniqueID())) && entityhuman.inventory.pickup(itemstack)) {
                  entityhuman.receive(this, i);
                  if (itemstack.isEmpty()) {
-@@ -294,6 +345,7 @@
+@@ -294,7 +345,9 @@
      }
  
      public void setItemStack(ItemStack itemstack) {
 +        com.google.common.base.Preconditions.checkArgument(!itemstack.isEmpty(), "Cannot drop air"); // CraftBukkit
          this.getDataWatcher().set(EntityItem.b, itemstack);
++        this.getDataWatcher().markDirty(EntityItem.b); // CraftBukkit - SPIGOT-4591, must mark dirty
      }
  
+     @Nullable