Safely handle cancelled inventory open events on vaults by checking if inventory is null AFTER it's opened. Resolves #354

src/main/java/com/drtshock/playervaults/vaultmanagement/VaultManager.java

@@ -78,7 +78,6 @@ public class VaultManager {
                 inv = i;
             }
         }
-        PlayerVaults.getInstance().getOpenInventories().put(info.toString(), inv);
 
         return inv;
     }