taglist not send to down stream if all the frame corrupted

Submitted by Jian Li

Link to original bug (#737246)

Description

I found in audiodecoder and videodecoder base, taglist only be sent to downstream when successfully decoded one frame.
But for some corrupted streams, all the frames maybe corrupted, decoder can get one valid frame util EOS. In this case, taglist will be missing in the pipeline, then application can get the track info from playbin.

I think it should check if there is still tags_changed when received EOS and drained all the data, if yes, send this tags to downstream.

A patch is attached, please check it.

Version: 1.2.3