[WAN_IP] Fall back to HTTP properly on DNS connection errors

[ingrinder]

Description

This is just a small change so that if dig returns a nonzero exit code, then we don't immediately return None as the IP.

Reason and / or context

For example on my home network I block outgoing port 53: As you see in this case archey fails to get the IP with the default settings and doesn't fall back to the configured HTTP URL :frowning_face:

How has this been tested ?

It now gets my IP and passes the additional test case I added

Types of changes :

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] Typo / style fix (non-breaking change which improves readability)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist :

• [ ] [IF NEEDED] I have updated the README.md file accordingly ;
• [X] [IF NEEDED] I have updated the test cases (which pass) accordingly ;
• [ ] [IF BREAKING] This pull request targets next Archey version branch ;
• [X] My changes looks good ;
• [X] I agree that my code may be modified in the future ;
• [X] My code follows the code style of this project (PEP8).