[BUG] Users Can Submit Candidates After Closing Poll

[ahoopes16]

Describe the bug
At time of writing, a user is able to submit a candidate even after someone runs the !!closepoll command. According to the State Transition table, this is meant to be an invalid command.

To Reproduce
Steps to reproduce the behavior:

1. Run !!startpoll and begin a poll
2. Submit a candidate
3. Run !!closepoll to close the poll
4. Submit another candidate
5. Observe that an error is not thrown

Expected behavior
An error message should display, explaining that the poll has already been closed and therefore the submission cannot be accepted.

Desktop (please complete the following information):

• OS: Windows 10
• Version 1.1.0