gst/avi/gstavidemux.*: For timestamping audio packets we need to take into account the amount of blocks in one entry ...

Original commit message from CVS:
* gst/avi/gstavidemux.c: (gst_avi_demux_parse_subindex),
(gst_avi_demux_parse_stream), (gst_avi_demux_parse_index):
* gst/avi/gstavidemux.h:
For timestamping audio packets we need to take into account the
amount of blocks in one entry using the blockalign. Fixes some sync
issues with zero-padded audio blocks in the beginning of avi files.