GstAudioEncoder: Do not drain and reset on new segment
It causes PTS and DTS to restart from 0 because priv->base_ts gets reset to GST_CLOCK_TIME_NONE. Downstream, at least mpegtsmux, would then print "ignoring DTS going backward" warning in loop.
GstVideoEncoder and GstAudioDecoder are not doing anything special on SEGMENT event, so this is at least more consistent.
Fixes: #1237
Edited by Xavier Claessens