d.vect: update error message

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@48126 15284696-431f-4ddb-bdfa-cd5b030d7da7

display/d.vect/main.c

@@ -424,7 +424,7 @@ int main(int argc, char **argv)
     chcat = 0;
     if (where_opt->answer) {
 	if (Clist->field < 1)
-	    G_fatal_error(_("Option <%s> must be > 0"), field_opt->key);
+	    G_fatal_error(_("Option <%s> requires option <%s> > 0"), where_opt->key, field_opt->key);
 	chcat = 1;
 	option_to_where(&Map, Clist, where_opt->answer);
     }