gh-1837 WEAVIATE-2 fix segfault by copying memory

[etiennedi]

This still requires a chaos-engineering pipeline to make sure this is
really fixed, so far manual testing seems to indicate that it is indeed
gone.

fixes #1837

[codecov]

Codecov Report

Merging #1843 (9280066) into master (4e1b648) will increase coverage by 0.05%.
The diff coverage is 67.85%.

@@            Coverage Diff             @@
##           master    #1843      +/-   ##
==========================================
+ Coverage   65.93%   65.98%   +0.05%     
==========================================
  Files         411      411              
  Lines       30884    30888       +4     
==========================================
+ Hits        20362    20382      +20     
+ Misses       8739     8716      -23     
- Partials     1783     1790       +7     

Flag	Coverage Δ
integration	67.23% <50.00%> (+0.12%)	⬆️
unittests	65.98% <67.85%> (+0.05%)	⬆️

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

Impacted Files	Coverage Δ
...ters/handlers/graphql/local/common_filters/bm25.go	0.00% <ø> (ø)
adapters/handlers/rest/middlewares.go	0.00% <0.00%> (ø)
adapters/repos/db/buffered_random_reader.go	70.83% <ø> (ø)
adapters/repos/db/inverted/bm25_searcher.go	0.00% <ø> (ø)
adapters/repos/db/inverted/prop_length_tracker.go	81.33% <ø> (ø)
adapters/repos/db/inverted/score_merger.go	100.00% <ø> (ø)
adapters/repos/db/inverted/stopwords/detector.go	40.74% <ø> (ø)
adapters/repos/db/lsmkv/binary_search_tree_map.go	97.29% <ø> (ø)
...os/db/lsmkv/segment_key_and_tombstone_extractor.go	84.37% <ø> (ø)
adapters/repos/db/lsmkv/strategies_map.go	56.87% <ø> (ø)
... and 17 more

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