fix nil pointer panic in system-probe config

[clamoriniere]

What does this PR do?

A brief description of the change being made with this pull request.

Motivation

What inspired you to submit this pull request?

Additional Notes

Anything else we should know when reviewing?

Describe your test plan

Write there any instructions and details you may have to test your PR.

[codecov-commenter]

Codecov Report

Merging #350 (e56ee39) into main (b0c187b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #350   +/-   ##
=======================================
  Coverage   64.36%   64.36%           
=======================================
  Files          62       62           
  Lines        6878     6879    +1     
=======================================
+ Hits         4427     4428    +1     
  Misses       2135     2135           
  Partials      316      316           

Flag	Coverage Δ
unittests	64.36% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
controllers/datadogagent/systemprobe.go	91.48% <100.00%> (+0.18%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b0c187b...e56ee39. Read the comment docs.