Fix (weights only) checkpoints loading without pl

[s-rog]

What does this PR do?

Fixes #2653

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[codecov]

Codecov Report

Merging #3287 into master will decrease coverage by 6%.
The diff coverage is 50%.

@@           Coverage Diff           @@
##           master   #3287    +/-   ##
=======================================
- Coverage      90%     84%    -6%     
=======================================
  Files          86      88     +2     
  Lines        8102    9079   +977     
=======================================
+ Hits         7310    7608   +298     
- Misses        792    1471   +679     

[SkafteNicki]

LGTM