change confusing warning to degub msg

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@42919 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.to.rast/do_areas.c

@@ -116,7 +116,7 @@ int sort_areas(struct Map_info *Map, struct line_pnts *Points, int field)
 	centroid = Vect_get_area_centroid(Map, i + 1);
 	if (centroid <= 0) {
 	    SETNULL(&cat);
-	    G_warning(_("Area without centroid (may be OK for island)"));
+	    G_debug(2,_("Area without centroid (OK for island)"));
 	}
 	else {
 	    Vect_read_line(Map, NULL, Cats, centroid);