[main] pgr_drivingDistance accepts negative distance without raising an error

[sakirr05]

While testing pgr_drivingDistance before updating the docs, I noticed that passing a negative distance doesn't raise an error — it just returns zero rows with a NOTICE. That's indistinguishable from a valid empty result.

pgRouting 4.0.1 | PostgreSQL 14.22 | Ubuntu 22.04

distance = -1.0 -> silent empty result:

distance = 0.0 -> returns origin node only:

Interestingly, on develop (4.1.0-dev) the same query raises:
ERROR: Negative value found on 'distance Must be positive

Note: I used claude's AI assistance to help structure the testing process