use .cash()

Author: haythemsellami

TODO

@@ -4,7 +4,6 @@
   * currently it's an arithmetic underflow
 ! Don't make quotes that would cause a swap to fail due to supply or borrow caps
 ! Use `myDebt() == 0` condition for disabling controller: more accurate
-! In _computeQuote() use vault.cash() method instead of token.balanceOf() otherwise donations could cause quoted swaps to fail
 ! In _computeQuote(), exactOut swaps should verify the *amount* (not quote) is withdrawable
 * ConstantSum: incorporate price multipliers in quote methods
 * natspec

src/MaglevBase.sol

@@ -200,10 +200,7 @@ abstract contract MaglevBase is IMaglevBase, EVCUtil {
         uint256 quote = computeQuote(amount, exactIn, asset0IsInput);
 
         require(quote <= (asset0IsInput ? reserve1 : reserve0), InsufficientReserves());
-        require(
-            quote <= IERC20(asset0IsInput ? asset1 : asset0).balanceOf(asset0IsInput ? vault1 : vault0),
-            InsufficientCash()
-        );
+        require(quote <= IEVault(asset0IsInput ? vault1 : vault0).cash(), InsufficientCash());
 
         // exactOut: increase required amountIn, rounding up
         if (!exactIn) quote = (quote * 1e18 + (feeMultiplier - 1)) / feeMultiplier;