Fix being unable to vote in polls without an expiration date (#39949)

app/javascript/mastodon/api_types/polls.ts

@@ -9,7 +9,7 @@ export interface ApiPollOptionJSON {
 
 export interface ApiPollJSON {
   id: string;
-  expires_at: string;
+  expires_at: string | null;
   expired: boolean;
   multiple: boolean;
   votes_count: number;

app/javascript/mastodon/components/poll.tsx

@@ -35,7 +35,7 @@ const messages = defineMessages({
 });
 
 const isPollExpired = (expiresAt: Model.Poll['expires_at']) =>
-  new Date(expiresAt).getTime() < Date.now();
+  expiresAt !== null && new Date(expiresAt).getTime() < Date.now();
 
 interface PollProps {
   pollId: string;
@@ -69,7 +69,7 @@ export const Poll: React.FC<PollProps> = ({
     return poll.expired || isPollExpired(poll.expires_at);
   }, [poll]);
   const timeRemaining = useMemo(() => {
-    if (!poll) {
+    if (!poll?.expires_at) {
       return null;
     }
     if (expired) {