ext/flac/gstflacdec.c: Don't try to seek beyond the end of the file (would occasionally display error dialogs in tote...

Original commit message from CVS:
* ext/flac/gstflacdec.c: (gst_flac_dec_handle_seek_event):
Don't try to seek beyond the end of the file (would
occasionally display error dialogs in totem when seeking
to the end) (#335869). Will still throw an error though
if the file is truncated and the total_samples value in
the stream header is wrong.