Only check SORT_TEMP_DIR if discoverable (JENA-977)
Only check SORT_TEMP_DIR if discoverable (JENA-977)

In some environments tdbloader2index may not be able to figure out what
the sort temp directory is going to be in which case we should skip
trying to check the available space on it

kamir/jena,apache/jena,tr3vr/jena,atsolakid/jena,tr3vr/jena,atsolakid/jena,CesarPantoja/jena,samaitra/jena,jianglili007/jena,jianglili007/jena,CesarPantoja/jena,apache/jena,samaitra/jena,atsolakid/jena,tr3vr/jena,apache/jena,kidaa/jena,tr3vr/jena,jianglili007/jena,samaitra/jena,jianglili007/jena,kamir/jena,CesarPantoja/jena,apache/jena,kidaa/jena,CesarPantoja/jena,kamir/jena,tr3vr/jena,atsolakid/jena,jianglili007/jena,CesarPantoja/jena,CesarPantoja/jena,kamir/jena,atsolakid/jena,samaitra/jena,tr3vr/jena,atsolakid/jena,kidaa/jena,CesarPantoja/jena,apache/jena,samaitra/jena,jianglili007/jena,apache/jena,kidaa/jena,apache/jena,jianglili007/jena,kidaa/jena,kidaa/jena,atsolakid/jena,tr3vr/jena,samaitra/jena,samaitra/jena,kamir/jena,kidaa/jena,kamir/jena,kamir/jena,apache/jena