fix: empty database causing the usage of undefined dashboard parameters

[devamin]

error screenshot :

stack :

2023-06-04 15:12:59.266 Uncaught app exception
Traceback (most recent call last):
  File "/Users/bkamine/miniconda3/envs/dashboard/lib/python3.9/site-packages/streamlit/runtime/scriptrunner/script_runner.py", line 565, in _run_script
    exec(code, module.__dict__)
  File "/Volumes/fs/code/hummingbot/dashboard/pages/2_🚀_Strategy_Performance.py", line 65, in <module>
    selected_exchange = st.selectbox("Select an exchange:", list(exchanges_trading_pairs.keys()))
NameError: name 'exchanges_trading_pairs' is not defined

[cardosofede]

One thing that I was thinking is, if there is no data probably we also want to create a st.warning explaining with a message for the user, what do you think?

[cardosofede]

@devamin I think that this configuration shouldn't be in the main branch, probably we have to exclude .vscode from the git ignore.