Added a setArmorContents method to PlayerInventory.

It handles error checking.  Null item stacks and air item stacks are both converted to clear slot calls to prevent crashing the client.

By: Raphfrk <raphfrk@gmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryPlayer.java

@@ -71,4 +71,18 @@ public class CraftInventoryPlayer extends CraftInventory implements PlayerInvent
         }
         return ret;
     }
+
+    public void setArmorContents(ItemStack[] items) {
+       int cnt = getSize();
+       if (items == null) {
+           items = new ItemStack[4];
+       }
+       for (ItemStack item : items) {
+           if (item == null || item.getTypeId() == 0) {
+               clear(cnt++);
+           } else {
+               setItem(cnt++, item);
+           }
+       }
+    }
 }