Hi,

While using Virtuoso v7.2.12 (built for GeoSPARQL support, as described in [readme](https://github.com/openlink/virtuoso-opensource/blob/develop/7/README.GeoSPARQL.md)) for GeoSPARQL operations involving a coordinate reference system transformation, I noticed the following:

Insert a `geo:Geometry` with a custom coordinate reference system, as described in [8.8.1.1 - Req 14](https://opengeospatial.github.io/ogc-geosparql/geosparql11/spec.html#geo:wktLiteral)
```sparql
PREFIX  geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

INSERT DATA {
    GRAPH <http://g> {
        <http://a> a geo:Geometry ;
        geo:asWKT "<www.opengis.net/def/crs/EPSG/0/31370> POINT (155822.2 132723.18)"^^<http://www.opengis.net/ont/geosparql#wktLiteral> .
    }
}
```
Above query errors with `Virtuoso 42000 Error RDFGE: RDF box with a geometry RDF type and a non-geometry content`

Workaround for insertion:
```sparql
PREFIX geo: <http://www.opengis.net/ont/geosparql#>

INSERT {
    GRAPH <http://g> {
        <http://a> a geo:Geometry ;
            geo:asWKT ?fullwkt .
    }
}
WHERE {
        ?s ?p ?o .
        BIND("POINT (155822.2 132723.18)" AS ?wkts)
        BIND(CONCAT("<http://www.opengis.net/def/crs/EPSG/0/31370> ", ?wkts) AS ?wktcrs)
        BIND(STRDT(?wktcrs, geo:wktLiteral) as ?fullwkt)
}
```
  
Now, when querying for the inserted data requesting format `text/turtle` (used `bif:st_transform` since [`geof:transform`](https://opengeospatial.github.io/ogc-geosparql/geosparql11/spec.html#_function_geoftransform) doesn't seem supported just yet ):
```sparql
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

CONSTRUCT { 
    <http://x> <http://y> ?origCrsWkt .
    <http://x> <http://y> ?wgs84Wkt .
    <http://x> <http://y> ?wgs84WktString .
}
WHERE {
    ?s a geo:Geometry ;
        geo:asWKT ?origCrsWkt .
    BIND(bif:st_transform (?origCrsWkt, 4326) AS ?wgs84Wkt)
    BIND(STR(?wgs84Wkt) as ?wgs84WktString)
}
```

We can see that the query works (including a correct crs-transform!)
However, when making the same query, but requesting format `application/json` instead, the produced json is invalid (notice the missing quotes):
```json
{
  "http://x" : { "http://y" : [ { "type" : "literal", "value" : POINT(4.4508225544308 50.505267305279) , "datatype" : "http://www.opengis.net/ont/geosparql#wktLiteral" } ,
      { "type" : "literal", "value" : "POINT(4.4508225544308 50.505267305279)" } ,
      { "type" : "literal", "value" : "SRID=31370;POINT(155822.2 132723.18)" , "datatype" : "http://www.openlinksw.com/schemas/virtrdf#Geometry" } ] }
}
```
`bif:st_transform` result breaks JSON result for `CONSTRUCT` query
This is a GitHub Issue
repo:virtuoso-opensource
owner:openlink
Title : `bif:st_transform` result breaks JSON result for `CONSTRUCT` query
Issue date:

--- start body ---
Hi,

While using Virtuoso v7.2.12 (built for GeoSPARQL support, as described in [readme](https://github.com/openlink/virtuoso-opensource/blob/develop/7/README.GeoSPARQL.md)) for GeoSPARQL operations involving a coordinate reference system transformation, I noticed the following:

Insert a `geo:Geometry` with a custom coordinate reference system, as described in [8.8.1.1 - Req 14](https://opengeospatial.github.io/ogc-geosparql/geosparql11/spec.html#geo:wktLiteral)
```sparql
PREFIX  geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

INSERT DATA {
    GRAPH <http://g> {
        <http://a> a geo:Geometry ;
        geo:asWKT "<www.opengis.net/def/crs/EPSG/0/31370> POINT (155822.2 132723.18)"^^<http://www.opengis.net/ont/geosparql#wktLiteral> .
    }
}
```
Above query errors with `Virtuoso 42000 Error RDFGE: RDF box with a geometry RDF type and a non-geometry content`

Workaround for insertion:
```sparql
PREFIX geo: <http://www.opengis.net/ont/geosparql#>

INSERT {
    GRAPH <http://g> {
        <http://a> a geo:Geometry ;
            geo:asWKT ?fullwkt .
    }
}
WHERE {
        ?s ?p ?o .
        BIND("POINT (155822.2 132723.18)" AS ?wkts)
        BIND(CONCAT("<http://www.opengis.net/def/crs/EPSG/0/31370> ", ?wkts) AS ?wktcrs)
        BIND(STRDT(?wktcrs, geo:wktLiteral) as ?fullwkt)
}
```
  
Now, when querying for the inserted data requesting format `text/turtle` (used `bif:st_transform` since [`geof:transform`](https://opengeospatial.github.io/ogc-geosparql/geosparql11/spec.html#_function_geoftransform) doesn't seem supported just yet ):
```sparql
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

CONSTRUCT { 
    <http://x> <http://y> ?origCrsWkt .
    <http://x> <http://y> ?wgs84Wkt .
    <http://x> <http://y> ?wgs84WktString .
}
WHERE {
    ?s a geo:Geometry ;
        geo:asWKT ?origCrsWkt .
    BIND(bif:st_transform (?origCrsWkt, 4326) AS ?wgs84Wkt)
    BIND(STR(?wgs84Wkt) as ?wgs84WktString)
}
```

We can see that the query works (including a correct crs-transform!)
However, when making the same query, but requesting format `application/json` instead, the produced json is invalid (notice the missing quotes):
```json
{
  "http://x" : { "http://y" : [ { "type" : "literal", "value" : POINT(4.4508225544308 50.505267305279) , "datatype" : "http://www.opengis.net/ont/geosparql#wktLiteral" } ,
      { "type" : "literal", "value" : "POINT(4.4508225544308 50.505267305279)" } ,
      { "type" : "literal", "value" : "SRID=31370;POINT(155822.2 132723.18)" , "datatype" : "http://www.openlinksw.com/schemas/virtrdf#Geometry" } ] }
}
```
--- end body ---
