xbps_find_orphan_packages: report return value as errno in an error path.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20091023120316-om71k2rnmk4ruzh1

lib/orphans.c

@@ -138,6 +138,7 @@ xbps_find_orphan_packages(void)
 	rv = xbps_callback_array_iter_reverse_in_dict(dict, "packages",
 	    find_orphan_pkg, NULL);
 	if (rv != 0) {
+		errno = rv;
 		cleanup();
 		return NULL;
 	}