added warning for not loading dataset

app.py

@@ -112,6 +112,8 @@ def main():
 
     # Search button
     if st.button("Search"):
+        if not df:
+            st.warning("You have not selected a Dataset. Please click on Load Dataset to load your respective Dataset")
         # Validate input
         if not query:
             st.warning("Please enter a search query.")