Make the wireguard plugin more robust against missing data

[pyrco]

(DIS-2353)

[codecov]

Codecov Report

Merging #407 (6beeb27) into main (c35096b) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

❗ Current head 6beeb27 differs from pull request most recent head 847816f. Consider uploading reports for the commit 847816f to get more accurate results

@@            Coverage Diff             @@
##             main     #407      +/-   ##
==========================================
- Coverage   73.76%   73.69%   -0.07%     
==========================================
  Files         252      251       -1     
  Lines       20188    20180       -8     
==========================================
- Hits        14892    14872      -20     
- Misses       5296     5308      +12     

Flag	Coverage Δ
unittests	73.69% <100.00%> (-0.07%)	⬇️

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Files	Coverage Δ
dissect/target/plugins/apps/vpns/wireguard.py	87.93% <100.00%> (+1.39%)	⬆️

... and 3 files with indirect coverage changes

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