ST_LocateBetweenElevations should return NULL and not fail if intersection is void

[vince]

The ST_LocateBetweenElevations () functions, instead of returning a NULL or empty geometry in case the object tested is not partly or totally included between the two given elevations, returns : "ERROR: The lwline_clip_to_ordinate_range returned null." and fails. It is thus impossible to use the function in a WHERE clause for discarding geometries:

WITH polygons AS (SELECT gid, (ST_Dump (geom)).geom AS geom FROM houses) SELECT gid FROM polygons WHERE NOT ST_IsEmpty (ST_LocateBetweenElevations (ST_ExteriorRing (geom), 70, 80));
ERROR:  The lwline_clip_to_ordinate_range returned null.

[pramsey]

Fixed in trunk at r8969. 1.5 at r8970