actually add the timecodeOffset when getting audio frames

We have to ask the AudioReencodeBuffer for audio to write with the
original timecode before applying the cut list.

Patch by Nicolas Pöhlmann
Reviewed by Paul Gardiner

Refs #11213
Refs #11639

(cherry picked from commit ea8c2b91e91e5cada8f8309f9fcb63f831f79aee)