fix: a recipient warning on the confirmation screen is about the recipient on screen (closes #575)

checkRecipientHistory() showed the warning boxes whenever its lookups
answered, so after Back and a review to another recipient, a late answer
about the first recipient could show the never-sent-a-transaction, contract
or Etherscan phishing box on the second recipient's screen. It now drops a
result for a transaction no longer on screen, as estimateGas() and
readBalances() already do.

tests/confirmTxLateResult.test.js holds back the first screen's answer until
the second screen is shown, for each of the three boxes, the balance read and
the fee estimate.

Model: opus-5-5

src/popup/views/confirmTx.js

@@ -609,6 +609,9 @@ async function checkRecipientHistory(txInfo) {
             fromAddress: txInfo.from,
             chainId: txInfo.chainId,
         });
+        // The user may have left this transaction while the checks were in
+        // flight; its warnings must not reach another recipient's screen.
+        if (pendingTx !== txInfo) return;
         for (const w of asyncWarnings) {
             if (w.type === "contract") {
                 $("confirm-contract-warning").style.visibility = "visible";