tport: do not refer NULL in case of error
tport: do not refer NULL in case of error

NULL was referenced if socket() system call failed.

Nokia CID 46240, 46241

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