[PostGIS] #6064: Silent topology corruption with topology.TopoGeo_addLinestring

[PostGIS]

#6064: Silent topology corruption with topology.TopoGeo_addLinestring
-----------------------+--------------------
  Reporter:  strk      |      Owner:  strk
      Type:  defect    |     Status:  new
  Priority:  medium    |  Milestone:
 Component:  topology  |    Version:  master
Resolution:            |   Keywords:
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Comment (by strk):

 The resulting topology contains edges that are very short:
 {{{
 postgis_reg=# select edge_id, ST_Length(geom) from t6064.edge;
  edge_id |       st_length
 ---------+------------------------
        6 |    0.20166820447100725
        1 | 2.5110321484918296e-07
        4 | 2.5110321655621793e-07
        3 |     0.2017140909558352
        2 | 3.1201241416250513e-13
        5 | 3.6487597516463005e-13
 }}}

 The computed snap tolerance (when NOT passing 0 as the tolerance) is
 `2.48862579345703e-13` so those tiny edges are still longer than
 tolerance.
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/6064#comment:3>
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