Critical bug fix to RariFundManager._withdrawFrom

Before this bug fix, RariFundManager._withdrawFrom may have burned more RFT than necessary when processing a user's withdrawal. After withdrawing from a pool, to update the pool balance cache, instead of subtracting the amount actually withdrawn from the pool, the total withdrawal amount was subtracted from the pool balance cache. This could have caused the cached fund balance used in the RFT burn amount calculation to be lower than it should have been, causing the amount of RFT burned to be higher than it should have been.

contracts/RariFundManager.sol

@@ -732,8 +732,8 @@ contract RariFundManager is Ownable {
             _rariFundController.withdrawFromPoolKnowingBalance(pool, currencyCode, poolAmount, poolBalance);
 
             if (pool == 0) {
-                for (uint256 j = 0; j < _dydxBalancesCache.length; j++) if (_dydxTokenAddressesCache[j] == erc20Contract) _dydxBalancesCache[j] = poolBalance.sub(amount);
-            } else _poolBalanceCache[currencyCode][pool] = poolBalance.sub(amount);
+                for (uint256 j = 0; j < _dydxBalancesCache.length; j++) if (_dydxTokenAddressesCache[j] == erc20Contract) _dydxBalancesCache[j] = poolBalance.sub(poolAmount);
+            } else _poolBalanceCache[currencyCode][pool] = poolBalance.sub(poolAmount);
 
             contractBalance = contractBalance.add(poolAmount);
         }