refactor: determine userInput by trimming

app/components/chat.tsx

@@ -480,7 +480,7 @@ export function Chat() {
 
   // submit user input
   const onUserSubmit = () => {
-    if (userInput.length <= 0) return;
+    if (userInput.trim() === "") return;
     setIsLoading(true);
     chatStore.onUserInput(userInput).then(() => setIsLoading(false));
     setBeforeInput(userInput);