Convert Plugin NoneType previous_sibling bug

[AngeloGiacco]

Describe the bug
Convert plugin produces the following error: 'NoneType' object has no attribute 'previous_sibling'. I believe this has something to do with beautiful soup but I am not sure. I suspect this because previous_sibling is not from my own code.

To Reproduce
Steps to reproduce the behavior:

1. Setup honeybot
2. Convert two currencies '.convert HUF EUR'
3. Wait, error is hit and miss, may need to execute command several times
4. See error in terminal

Expected behavior
Expected behaviour usually happens which is showing the currency conversion. In this case, how many EUR in one HUF. However, sometimes it shows an error.

Screenshots

Desktop (please complete the following information):

• OS: macOS
• Using Adium to connect to IRC