config: Skip magwell check if no prefix defined

[PabstMirror]

e.g. CBA repo

this should only be running for magazines that start with CBA
So I assume the prefix isn't loaded and is defaulting to "", which matches all mags?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.6%. Comparing base (62cc0ba) to head (0b91ae7).

Additional details and impacted files

Files with missing lines	Coverage Δ
.../src/analyze/lints/c09_magwell_missing_magazine.rs	61.1% <100.0%> (+0.2%)	⬆️