gst/id3demux/gstid3demux.c: Make sure we don't return GST_FLOW_OK with a NULL buffer in certain cases where a read be...

Original commit message from CVS:
* gst/id3demux/gstid3demux.c: (gst_id3demux_trim_buffer),
(gst_id3demux_read_range):
Make sure we don't return GST_FLOW_OK with a NULL buffer in
certain cases where a read beyond the end of the file is
requested. Fixes #345930.
* gst/apetag/gsttagdemux.c: (gst_tag_demux_trim_buffer),
(gst_tag_demux_read_range):
Fix same issue here as well.