Several places look up a multimap with find(key) and then iterate while
iter->first == key, assuming find() returns the first element with that key.
The standard does not guarantee this, and recent libc++ (Apple clang 21 /
libc++ 2200) returns an arbitrary matching element. graph::findLink() then
misses existing links and Optimizer::getConnectedGraph() aborts with
"Condition (kter!=linksIn.end()) not met!" on graphs with loop closures or
multiple sessions (rtabmap-export --opt 0, rtabmap-reprocess, etc.).
Replace find() with lower_bound() at those sites and add a regression test.
Co-authored-by: Claude Opus 5.5 (1M context) <[email protected]>
Co-authored-by: matlabbe <[email protected]>
