Crash during test

[niamtokik]

cozolib_c is crashing during a test.

thread '<unnamed>' panicked at 'index out of bounds: the len is 0 but the index is 0', cozo-core/src/fixed_rule/algos/all_pairs_shortest_path.rs:80:24
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5
Aborted

when executing this test:

?IQUERY_LOG(Db, "centrality[code, score] <~ BetweennessCentrality(*route[a, b])"
  "?[code, desc, score] := centrality[code, score], *airport{code, desc}"
  ":limit 10;"
  ":order -score"),