nua_stack.c: fixed klocwork issues
nua_stack.c: fixed klocwork issues

darcs-hash:20080522104707-65a35-024044c3ed52ea1e8b95040470885d03399d925e.gz

BelledonneCommunications/sofia-sip,unispeech/sofia-sip,xhook/sofia-sip,xhook/sofia-sip,erdincay/sofia-sip,xhook/sofia-sip,erdincay/sofia-sip,xhook/sofia-sip,jart/sofia-sip,erdincay/sofia-sip,jart/sofia-sip,jart/sofia-sip,unispeech/sofia-sip,erdincay/sofia-sip,BelledonneCommunications/sofia-sip,unispeech/sofia-sip,unispeech/sofia-sip,xhook/sofia-sip,BelledonneCommunications/sofia-sip,BelledonneCommunications/sofia-sip