remove unnecessary judgment

app/components/chat.tsx

@@ -404,7 +404,6 @@ export function Chat(props: {
 
   // submit user input
   const onUserSubmit = () => {
-    if (userInput.length <= 0) return;
     setIsLoading(true);
     chatStore.onUserInput(userInput).then(() => setIsLoading(false));
     setUserInput("");