kamailio-4.x: add fix for CVE-2018-14767

kamailio-4.x: add fix for CVE-2018-14767

CVE-2018-14767: "In Kamailio before 5.0.7 and 5.1.x before 5.1.4, a
crafted SIP message with a double "To" header and an empty "To" tag
causes a segmentation fault and crash. The reason is missing input
validation in the "build_res_buf_from_sip_req" core function. This could
result in denial of service and potentially the execution of arbitrary
code."

Patch from upstream. Path to msg_translator.c amended.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>