fix(drivingDistance): raise error on negative distance input

[aki1770-del]

Summary

pgr_drivingDistance and pgr_drivingDistanceWithPoints silently returned an empty result set when called with a negative distance value. An empty result is indistinguishable from a valid empty-graph result — callers have no way to detect the misconfiguration.

The develop branch (4.1.0-dev) already raises ERROR: Negative value found on 'distance' via src/spanningTree/spanningTree_process.cpp:105-106. This PR backports the equivalent guard to main.

Fix

Added a negative-distance guard in pgr_do_drivingDistance and pgr_do_drivingDistanceWithPoints (both C++ drivers) before graph query execution:

if (distance < 0) {
    *err_msg = to_pg_msg("Negative value found on 'distance'");
    *log_msg = to_pg_msg("distance must be non-negative");
    return;
}

Existing behavior audit (OPS-RULE-016)

• src/driving_distance/driving_distance_driver.cpp: no distance validation before graph construction; negative values silently traverse an empty Dijkstra result
• src/driving_distance/driving_distance_withPoints_driver.cpp: same pattern, same missing guard
• src/spanningTree/spanningTree_process.cpp (develop branch, line 105-106): contains the fix; does not exist on main

Scope classification (OPS-RULE-017)

(a) Bug fix — missing input validation that causes silent incorrect behavior.

Prior art consulted (OPS-RULE-018)

1. develop branch src/spanningTree/spanningTree_process.cpp:82-106 — the exact validation pattern this fix mirrors for the main branch
2. Issue #3091 — bug report with reproduce steps and confirmation of the develop-vs-main discrepancy
3. pgtap/dijkstra/driving_distance/edge_cases/issue_519.pg — existing edge-case test pattern followed for the new issue_3091.pg test

Test evidence

Added pgtap/dijkstra/driving_distance/edge_cases/issue_3091.pg:

• Asserts throws_ok for distance = -1.0
• Asserts distance = 0.0 returns only the origin node (valid edge case)

AI-assisted — authored with Claude, reviewed by Komada.

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