{audio,video}aggregator: Add has_internal_buffer vfunc
Implement GstAggregator::has_internal_buffer vfunc to inform pad's drained state, since Gst{Audio,Video}AggregatorPad has private buffer.
Closes gst-plugins-bad#786
Implement GstAggregator::has_internal_buffer vfunc to inform pad's drained state, since Gst{Audio,Video}AggregatorPad has private buffer.
Closes gst-plugins-bad#786