nua_event_server.c: fixed klocwork issue

darcs-hash:20080520114610-65a35-49d3ac5ebf84df47f42006df2af81698fb253830.gz

libsofia-sip-ua/nua/nua_event_server.c

@@ -145,7 +145,7 @@ nea_event_t *nh_notifier_event(nua_handle_t *nh,
 
   if (ev == NULL) {
     char *o_type = su_strdup(home, event->o_type);
-    char *o_subtype = strchr(o_type, '.');
+    char *o_subtype = o_type ? strchr(o_type, '.') : NULL;
 
     if (o_subtype)
       *o_subtype++ = '\0';