Add some additional sanity checks to excess collateral deposit

Author: kanewallmann

contracts/contract/minipool/RocketMinipoolDelegate.sol

@@ -405,9 +405,12 @@ contract RocketMinipoolDelegate is RocketMinipoolStorageLayout, RocketMinipoolIn
         // Only the owner can destroy a minipool
         require(nodeWithdrawalAddress == msg.sender || nodeAddress == msg.sender, "Only node operator can destroy minipool");
         // Send any remaining balance to rETH contract
-        payable(rocketTokenRETH).transfer(address(this).balance.sub(refundAmount));
-        // Send any overcollateralised ETH to the deposit pool
-        RocketTokenRETHInterface(rocketTokenRETH).depositExcessCollateral();
+        uint256 userAmount = address(this).balance.sub(refundAmount);
+        if (userAmount > 0) {
+            payable(rocketTokenRETH).transfer(userAmount);
+            // Send any overcollateralised ETH to the deposit pool
+            RocketTokenRETHInterface(rocketTokenRETH).depositExcessCollateral();
+        }
         // Self destruct the refund amount to node withdrawal address
         selfdestruct(payable(nodeWithdrawalAddress));
     }

contracts/contract/token/RocketTokenRETH.sol

@@ -142,11 +142,14 @@ contract RocketTokenRETH is RocketBase, ERC20, RocketTokenRETHInterface {
         uint256 targetCollateralRate = rocketDAOProtocolSettingsNetwork.getTargetRethCollateralRate();
         // Check if we are in excess
         if (collateralRate > targetCollateralRate) {
-            // Calculate ETH excess
+            // Calculate our target collateral in ETH
             uint256 targetCollateral = address(this).balance.mul(targetCollateralRate).div(collateralRate);
-            uint256 excessCollateral = address(this).balance.sub(targetCollateral);
-            // Send excess to deposit pool
-            rocketDepositPool.recycleExcessCollateral{value: excessCollateral}();
+            // If we have excess
+            if (address(this).balance > targetCollateral) {
+                // Send that excess to deposit pool
+                uint256 excessCollateral = address(this).balance.sub(targetCollateral);
+                rocketDepositPool.recycleExcessCollateral{value: excessCollateral}();
+            }
         }
     }