Crash with TopoGeo_addPoint

[strk]

Testcase:

SELECT NULL FROM topology.CreateTopology ('topo');                                                                                                                                             
SELECT NULL FROM topology.TopoGeo_addLinestring('topo', 'LINESTRING(0 0, 10 0)');                                                                                                              
SELECT NULL FROM topology.TopoGeo_addPoint('topo', 'POINT(9 5)', 5); 

PostGIS-3.4 is not affected, crashers are from 3.5 onward. Must be the experimental code doing edge merges.

[strk]

==105313== Use of uninitialised value of size 8
==105313==    at 0x13DC9534: lwgeom_closest_point (measures.c:57)
==105313==    by 0x13DBAFED: _lwt_SplitAllEdgesToNewNode (lwgeom_topo.c:6576)
==105313==    by 0x13DBAFED: _lwt_AddPoint (lwgeom_topo.c:6859)
==105313==    by 0x13D745F1: UnknownInlinedFun (postgis_topology.c:5042)
==105313==    by 0x13D745F1: TopoGeo_AddPoint (postgis_topology.c:4976)
==105313==    by 0x468B2C: ExecMakeTableFunctionResult (in /usr/lib/postgresql/16/bin/postgres)
==105313==    by 0x47A659: ??? (in /usr/lib/postgresql/16/bin/postgres)
==105313==    by 0x469499: ExecScan (in /usr/lib/postgresql/16/bin/postgres)
==105313==    by 0x45ABAC: standard_ExecutorRun (in /usr/lib/postgresql/16/bin/postgres)
==105313==    by 0x63D654: ??? (in /usr/lib/postgresql/16/bin/postgres)
==105313==    by 0x63F015: PortalRun (in /usr/lib/postgresql/16/bin/postgres)
==105313==    by 0x63FEA8: ??? (in /usr/lib/postgresql/16/bin/postgres)
==105313==    by 0x642BC6: PostgresMain (in /usr/lib/postgresql/16/bin/postgres)
==105313==    by 0x642D73: PostgresSingleUserMain (in /usr/lib/postgresql/16/bin/postgres)

[strk]

The crash is due to none of the edges found to be within tolerance using lwt_be_getEdgeWithinDistance2D being *closer* than tolerance (which the snapping code is using). It can only be reproduced by specifying a tolerance which equals exactly the distance from the closest edge.

[Sandro Santilli <strk@…>]

In cfc46e4/git:

Fix crash in TopoGeo_addPoint

References #5794 in master branch (3.6.0dev)
Includes regress test

[Sandro Santilli <strk@…>]

In 0b55ff4/git:

Fix crash in TopoGeo_addPoint

Closes #5794 in 3.5 branch (3.5.1dev)
Includes regress test