prevent setting backup withdrawal address to any deposit/backup address currently in use by minipool

Author: moles1

contracts/RocketUser.sol

@@ -272,9 +272,13 @@ contract RocketUser is RocketBase {
     function userSetWithdrawalDepositAddress(address _newUserAddressUsedForDeposit, address _miniPoolAddress) public returns(bool) {
         // Check backup withdrawal address is valid
         require(_newUserAddressUsedForDeposit != 0);
-        require(_newUserAddressUsedForDeposit != msg.sender);
         // Get an instance of that pool contract
         rocketPoolMini = RocketPoolMini(_miniPoolAddress);       
+        // Check user exists in minipool
+        require(rocketPoolMini.getUserExists(msg.sender));
+        // Check backup withdrawal address is not already in use
+        require(!rocketPoolMini.getUserExists(_newUserAddressUsedForDeposit));
+        require(!rocketPoolMini.getUserBackupAddressExists(_newUserAddressUsedForDeposit));
         // User can only set this backup address before deployment to casper, also partners cannot set this address to their own to prevent them accessing the users funds after the set withdrawal backup period expires
         if ((rocketPoolMini.getStatus() == 0 || rocketPoolMini.getStatus() == 1) && rocketPoolMini.getUserPartner(msg.sender) != _newUserAddressUsedForDeposit) {
             if (rocketPoolMini.setUserAddressBackupWithdrawal(msg.sender, _newUserAddressUsedForDeposit)) {