Ignore spurious REGISTER requests

Ignore spurious REGISTER requests

If a REGISTER request with a Call-ID matching an existing transaction is received
it was possible that the REGISTER request would overwrite the initreq of the
private structure. This info is used to generate messages for other responses in
the transaction. This patch ignores REGISTER requests that match non-REGISTER
transactions.

(closes issue #18051)
Reported by: eeman
Tested by: twilson

Review: https://reviewboard.asterisk.org/r/1050/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@297959 65c4cc65-6c06-0410-ace0-fbb531ad65f3