Fix time_measurement for empty events after deleter deleted the event

[dtrai2]

Fix writing time measurements into the event after the deleter has deleted the event. The bug only
happened when the metrics.measure_time.append_to_event configuration was set to true.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.09% 🎉

Comparison is base (11f1442) 92.28% compared to head (6cada15) 92.38%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #437      +/-   ##
==========================================
+ Coverage   92.28%   92.38%   +0.09%     
==========================================
  Files         133      133              
  Lines        9595     9597       +2     
==========================================
+ Hits         8855     8866      +11     
+ Misses        740      731       -9     

Files Changed	Coverage Δ
logprep/util/time_measurement.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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