lwgeom_free not empty safe

[robe]

SELECT ST_CollectionExtract(foo1.the_geom, 3) 
  FROM ((SELECT ST_GeomFromText('GEOMETRYCOLLECTION EMPTY',4326) As the_geom
  UNION ALL SELECT ST_GeomFromText('POLYGON EMPTY',4326) As the_geom
)
) As foo1
LIMIT 3;

Crashes server.

[pramsey]

In fact, the problem is a little deeper. Hard to believe we don't do this in other places, but it seems to be a generic problem with freeing empties, or more to the point, that the lwgeom's returned by pglwgeom_deserialize aren't constructed in such a way we can free them safely. More investigation req'd.

[pramsey]

Fixed up de-serialization routines to avoid *geoms = malloc(0) cases which were causing free to fail later on down the line (r5099)