gst/matroska/ebml-read.c: Change some GST_ELEMENT_ERRORs to GST_ERROR_OBJECT to make it possible to ignore errors and...

Original commit message from CVS:
* gst/matroska/ebml-read.c: (gst_ebml_read_element_id),
(gst_ebml_read_element_length), (gst_ebml_read_uint),
(gst_ebml_read_sint), (gst_ebml_read_float),
(gst_ebml_read_header):
Change some GST_ELEMENT_ERRORs to GST_ERROR_OBJECT to make it
possible to ignore errors and not post any ERROR messages on
the bus.
* gst/matroska/matroska-demux.c:
(gst_matroska_demux_parse_contents):
Ignore any errors and not just EOS when parsing the contents of
a SeekHead. Errors here are usually caused by truncated files
and playback of the file works fine. Fixes playback of the
audio_only_chapter_seekbroken.mka file from the MPlayer samples
archive.