Fixed argument checking in nta/nta.c.
Fixed argument checking in nta/nta.c.

Checking for invalid arguments in nta_incoming_treply() and
nta_incoming_mreply().

darcs-hash:20051028162846-65a35-c17b29a0eba5a2b19b25cbf9b36a00dabcd20011.gz

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