dcaparse: don't mark buffer as discont if space before is just zero padding
@Knopp
Submitted by Matej Link to original bug (#792186)
Description
There seem to be files out there that have zero padded buffers, gstreamer
marks them as discont, which causes decoder flush and decoding artifacts
Sample file
https://s3.amazonaws.com/MatejK/Samples/dts_sfx_long_core_1080p-thedigitaltheater.mkv