Agent crash using Dropbox listener

[eaglefn]

Note: Please fill out all sections (if applicable) and do not delete the below section headers, otherwise the bot will close the issue.

Empire Version

• Empire 3.x

OS Information (Linux flavor, Python version)

• OS:
• Python:

Describe the bug

A clear and concise description of what the bug is.

To Reproduce

Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior

A clear and concise description of what you expected to happen.

Screenshots

If applicable, add screenshots to help explain your problem.

Additional context

Add any other context about the problem here.

[Cx01N]

Closing since this looks like this is a duplicate of #354 and is missing information