Fixed su_clone_start() return value.

darcs-hash:20050908153512-65a35-42052087ebdcbbaab751bbf0b1329ec6b7869c4a.gz

libsofia-sip-ua/su/su_root.c

@@ -1010,7 +1010,7 @@ int su_clone_start(su_root_t *parent,
 #if !SU_HAVE_PTHREADS
   else {
     /* if we don't have threads, we *must* have parent root */
-    return NULL;
+    return -1;
   }
 #endif