Prevent confirming blank suggested token (#8909)

The "confirm suggested token" page allowed the confirm button to be
pressed even when there were no tokens to confirm. This can happen
sometimes when the page is in the process of redirecting.

ui/app/pages/confirm-add-suggested-token/confirm-add-suggested-token.component.js

@@ -122,6 +122,7 @@ export default class ConfirmAddSuggestedToken extends Component {
               type="secondary"
               large
               className="page-container__footer-button"
+              disabled={pendingTokens.length === 0}
               onClick={() => {
                 addToken(pendingToken)
                   .then(() => removeSuggestedTokens())