fix typeerror?

Author: adonesky1

src/SmartTransactionsController.ts

@@ -310,7 +310,7 @@ export default class SmartTransactionsController extends PollingControllerV1<
 
     if (isNewSmartTransaction) {
       // add smart transaction
-      const cancelledNonceIndex = currentSmartTransactions.findIndex(
+      const cancelledNonceIndex = currentSmartTransactions?.findIndex(
         (stx: SmartTransaction) =>
           stx.txParams?.nonce === smartTransaction.txParams?.nonce &&
           stx.status?.startsWith('cancelled'),