fix: a zero-minimum balance check never sets the output side (closes #649)

A BALANCE_CHECK_ERC20 of the sender with a zero minimum guarantees
nothing, and neither does one the router lets fail. Such a check set
Token Out and the minimum whenever the output side held no minimum.
After an UNWRAP_WETH that drops the minimum, a zero check of USDC
named USDC as Token Out. Such a check now sets neither line. A check
with a positive minimum is unchanged.

Model: opus-5-5

tests/uniswap.test.js

@@ -4380,10 +4380,9 @@ describe("uniswap decoder", () => {
         expect(detail(result, "Min. received").value).toBe("2.0000 USDC");
     });
 
-    // With no minimum stated before it, a zero balance check is what sets the
-    // output side, and it guarantees nothing. No step pays anyone, so the
-    // minimum is not said to be received.
-    test("a zero balance check with no earlier minimum states no minimum", () => {
+    // A zero balance check sets neither Token Out nor the minimum. The route
+    // pays only the WRAP_ETH's WETH, to the router, where it stays.
+    test("a zero balance check after a WRAP_ETH into the router names no output token and no minimum", () => {
         const data = buildExecute(
             solidityPacked(["uint8", "uint8"], [0x0b, 0x0e]),
             [
@@ -4396,9 +4395,16 @@ describe("uniswap decoder", () => {
         const result = uniswap.decode(data, ROUTER_ADDR, "0x1", {}, USER_ADDR);
         expect(result).not.toBeNull();
 
-        expect(detail(result, "Token Out").value).toContain("USDT");
-        expect(detail(result, "Min. paid out").value).toBe(
-            "None (no minimum guaranteed)",
+        expect(detail(result, "Token Out").value).toBe(
+            "Unknown (not named in the calldata)",
+        );
+        expect(detail(result, "Min. paid out")).toBeUndefined();
+        expect(detail(result, "Min. received")).toBeUndefined();
+        expect(detail(result, "Paid to").value).toBe(
+            "The router, where it stays (no later step pays it out)",
+        );
+        expect(detail(result, "Token moved into the router").address).toBe(
+            WETH_ADDR,
         );
     });