Ask User to Load a key first

[TanmayArya-1p]

if a key is not loaded into PasswordManager and the user tries to perform another task, For instance: creating a password file , An error is thrown and the program exits

Steps to Reproduce:

• Run the program and enter choice 3 without loading a key

PS C:\Users\Tanma\Documents\CodingRepos\PwManager> python main.py
What would you like to do?
          1. Create a new key
          2. Load an existing key
          3. Create a new password file
          4. Load an existing password file
          5. Add a password
          6. Get a password
          q. Quit

Enter choice: 3
Key not loaded. Please load a key first.
Invalid choice. Please try again.
Enter choice: 4
Key not loaded. Please load a key first.
Invalid choice. Please try again.
Enter choice: Traceback (most recent call last):
  File "C:\Users\Tanma\Documents\CodingRepos\PwManager\main.py", line 59, in <module>
    if __name__ == '__main__':
        ^^^^^^
  File "C:\Users\Tanma\Documents\CodingRepos\PwManager\main.py", line 31, in main
    while not done:
                 ^^^
KeyboardInterrupt
PS C:\Users\Tanma\Documents\CodingRepos\PwManager> ^C
PS C:\Users\Tanma\Documents\CodingRepos\PwManager> python main.py
What would you like to do?
          1. Create a new key
          2. Load an existing key
          3. Create a new password file
          4. Load an existing password file
          5. Add a password
          6. Get a password
          q. Quit

Enter choice: 3
Enter password file path: hello
Traceback (most recent call last):
  File "C:\Users\Tanma\Documents\CodingRepos\PwManager\main.py", line 60, in <module>
    main()
  File "C:\Users\Tanma\Documents\CodingRepos\PwManager\main.py", line 41, in main
    pm.create_password_file(path, password)
  File "C:\Users\Tanma\Documents\CodingRepos\PwManager\manager.py", line 27, in create_password_file
    self.add_password(site, password)
  File "C:\Users\Tanma\Documents\CodingRepos\PwManager\manager.py", line 40, in add_password
    encrypted = Fernet(self.key).encrypt(password.encode()).decode()
                ^^^^^^^^^^^^^^^^
  File "C:\Users\Tanma\AppData\Local\Programs\Python\Python312\Lib\site-packages\cryptography\fernet.py", line 34, in __init__
    key = base64.urlsafe_b64decode(key)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Tanma\AppData\Local\Programs\Python\Python312\Lib\base64.py", line 132, in urlsafe_b64decode
    s = _bytes_from_decode_data(s)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Tanma\AppData\Local\Programs\Python\Python312\Lib\base64.py", line 45, in _bytes_from_decode_data      
    raise TypeError("argument should be a bytes-like object or ASCII "
TypeError: argument should be a bytes-like object or ASCII string, not 'NoneType'
PS C:\Users\Tanma\Documents\CodingRepos\PwManager>