fix: (TychoRouter) Revert if empty swaps

- This is for security purposes. Max uncovered a vulnerability where funds could be stolen if we don't ether the while loop (i.e. if we have empty swaps).

foundry/src/TychoRouter.sol

@@ -17,6 +17,7 @@ import {LibSwap} from "../lib/LibSwap.sol";
 
 error TychoRouter__WithdrawalFailed();
 error TychoRouter__AddressZero();
+error TychoRouter__EmptySwaps();
 error TychoRouter__NegativeSlippage(uint256 amount, uint256 minAmount);
 error TychoRouter__AmountInNotFullySpent(uint256 leftoverAmount);
 error TychoRouter__MessageValueMismatch(uint256 value, uint256 amount);
@@ -191,6 +192,10 @@ contract TychoRouter is
         internal
         returns (uint256)
     {
+        if (swaps_.length == 0) {
+            revert TychoRouter__EmptySwaps();
+        }
+
         uint256 currentAmountIn;
         uint256 currentAmountOut;
         uint8 tokenInIndex = 0;

foundry/test/TychoRouter.t.sol

@@ -672,6 +672,13 @@ contract TychoRouterTest is TychoRouterTestSetup {
         assertGe(finalBalance, expAmountOut);
     }
 
+    function testEmptySwapsRevert() public {
+        uint256 amountIn = 10 ** 18;
+        bytes memory swaps = "";
+        vm.expectRevert(TychoRouter__EmptySwaps.selector);
+        tychoRouter.exposedSwap(amountIn, 2, swaps);
+    }
+
     function testSingleSwapIntegration() public {
         // Test created with calldata from our router encoder, replacing the executor
         // address with the USV2 executor address.