rtpgstdepay: Properly handle backward compat for event deserialization
Actual code is checking for a NULL terminator and a ';' terminator, for backward compat, in a chained way that cause all events being rejected. The proper condition is to reject the events when terminator isn't in ['\0', ';'] set. https://bugzilla.gnome.org/show_bug.cgi?id=758151