gstrtspconnection: Security loophole making heap overflow

The former code allowed an attacker to create a heap overflow by sending a longer than allowed session id in a response and including a semicolon to change the maximum length. With this change, the parser will never go beyond 512 bytes.

enabled an automatic merge when the pipeline for f6722775 succeeds

added Needs backport label

merged

added 1.14 label

added Backported into 1.16 label and removed Needs backport label

Gitlab won't let me set milestone %1.15.90 on this because the original repo disappeared (looks like it was deleted and re-created).