Quick fix for OOM issue with transitive paths

[hannahbast]

Fixes #1606 .

TODO: Currently only works when the start side of the transitive path operation has an empty local vocab (which is typically the case).

[RobinTF]

@hannahbast

Maybe for the case of empty vocabs this patch works better:

diff --git a/src/engine/LocalVocab.h b/src/engine/LocalVocab.h
index 3055c400..8190b72d 100644
--- a/src/engine/LocalVocab.h
+++ b/src/engine/LocalVocab.h
@@ -97,6 +97,9 @@ class LocalVocab {
   void mergeWith(const R& vocabs) {
     auto inserter = std::back_inserter(otherWordSets_);
     for (const auto& vocab : vocabs) {
+      if (vocab.empty()) {
+        continue;
+      }
       std::ranges::copy(vocab.otherWordSets_, inserter);
       *inserter = vocab.primaryWordSet_;
     }

[sparql-conformance]

Conformance check passed ✅

Test Status Changes 📊

Number of Tests	Previous Status	Current Status
6	Failed	Passed

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=3dc846a513d5ec8ddbc7f4718ea561dd93242dd2&prev=39ca684ae4e97f315eb0f1f198654547764d7c10

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 89.29%. Comparing base (39ca684) to head (3dc846a).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/engine/TransitivePathImpl.h	25.00%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1622      +/-   ##
==========================================
- Coverage   89.30%   89.29%   -0.01%     
==========================================
  Files         373      373              
  Lines       35377    35383       +6     
  Branches     3999     4000       +1     
==========================================
+ Hits        31594    31597       +3     
- Misses       2493     2497       +4     
+ Partials     1290     1289       -1     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[RobinTF]

Closing for #1621