SPIGOT-3144: Add missing PrepareAnvilEvent call.

By: md_5 <git@md-5.net>

paper-server/nms-patches/ContainerAnvil.patch

@@ -51,6 +51,15 @@
                  } else {
                      if (!flag && (itemstack1.getItem() != itemstack2.getItem() || !itemstack1.f())) {
 -                        this.g.setItem(0, ItemStack.a);
++                        org.bukkit.craftbukkit.event.CraftEventFactory.callPrepareAnvilEvent(getBukkitView(), ItemStack.a); // CraftBukkit
+                         this.a = 0;
+                         return;
+                     }
+@@ -245,7 +254,7 @@
+                     }
+ 
+                     if (flag2 && !flag1) {
+-                        this.g.setItem(0, ItemStack.a);
 +                        org.bukkit.craftbukkit.event.CraftEventFactory.callPrepareAnvilEvent(getBukkitView(), ItemStack.a); // CraftBukkit
                          this.a = 0;
                          return;