UX improve - allow leaderboard selection for the 2nd time

src/app.py

@@ -268,7 +268,7 @@ def main():
     if uploaded_file is not None:
         st.session_state.results_file = uploaded_file
 
-    if st.session_state.results_file is None:
+    if uploaded_file is None:
         st.write("Or:")
         if st.button("Choose from leaderboard"):
             choose_input_file_from_leaderboard()