SPIGOT-2495: Better validation of Skulls.

nms-patches/ItemSkull.patch

@@ -0,0 +1,10 @@
+--- a/net/minecraft/server/ItemSkull.java
++++ b/net/minecraft/server/ItemSkull.java
+@@ -117,6 +117,7 @@
+             nbttagcompound.set("SkullOwner", GameProfileSerializer.serialize(new NBTTagCompound(), gameprofile));
+             return true;
+         } else {
++            nbttagcompound.remove("SkullOwner"); // CraftBukkit - remove broken skulls
+             return false;
+         }
+     }