fix: null checking issue in exam entry

[Zacharis278]

Hidden code issue uncovered by #147

This will error if the learner has no attempts on the exam section. I moved this line to a point where we've already checked that an exam attempt exists. Actually this is already checked earlier in the function, the value would always be false.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.16%. Comparing base (c41adcb) to head (07b92a5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #148      +/-   ##
==========================================
- Coverage   94.16%   94.16%   -0.01%     
==========================================
  Files          68       68              
  Lines        1080     1079       -1     
  Branches      294      295       +1     
==========================================
- Hits         1017     1016       -1     
  Misses         58       58              
  Partials        5        5              

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