AST-2013-005: Fix crash caused by invalid SDP

If the SIP channel driver processes an invalid SDP that defines media
descriptions before connection information, it may attempt to reference
the socket address information even though that information has not yet
been set. This will cause a crash.

This patch adds checks when handling the various media descriptions that
ensures the media descriptions are handled only if we have connection
information suitable for that media.

Thanks to Walter Doekes, OSSO B.V., for reporting, testing, and providing
the solution to this problem.

(closes issue ASTERISK-22007)
Reported by: wdoekes
Tested by: wdoekes
patches:
  issueA22007_sdp_without_c_death.patch uploaded by wdoekes (License 5674)
........

Merged revisions 397756 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/10@397757 f38db490-d61c-443f-a65b-d21fe96a405b