SPIGOT-5449: Fix issue with projectiles

nms-patches/EntityProjectileThrowable.patch

@@ -0,0 +1,13 @@
+--- a/net/minecraft/server/EntityProjectileThrowable.java
++++ b/net/minecraft/server/EntityProjectileThrowable.java
+@@ -18,8 +18,8 @@
+ 
+     public void setItem(ItemStack itemstack) {
+         if (itemstack.getItem() != this.i() || itemstack.hasTag()) {
+-            this.getDataWatcher().set(EntityProjectileThrowable.e, SystemUtils.a((Object) itemstack.cloneItemStack(), (itemstack1) -> {
+-                itemstack1.setCount(1);
++            this.getDataWatcher().set(EntityProjectileThrowable.e, SystemUtils.a(itemstack.cloneItemStack(), (itemstack1) -> { // CraftBukkit - decompile error
++                if (!itemstack1.isEmpty()) itemstack1.setCount(1); // CraftBukkit
+             }));
+         }
+