v.external.out: skip pg options if not defined

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@51122 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.external.out/link.c

@@ -31,6 +31,7 @@ void make_link(const char *dsn,
     }
     
     /* parse options for PG data format */
+    pg_schema = pg_fid = pg_geom_name = NULL;
     if (options && *options && !use_ogr) {
 	pg_schema    = get_option_pg(options, "schema");
 	pg_fid       = get_option_pg(options, "fid");