ext/flac/gstflacdec.*: Handle segment seeks that include the end of the file as stop point properly: when the decoder...

Original commit message from CVS:
* ext/flac/gstflacdec.c: (gst_flac_dec_loop):
* ext/flac/gstflacdec.h:
Handle segment seeks that include the end of the file as stop point
properly: when the decoder hits EOS we want to send a SEGMENT_DONE
message instead of an EOS event in case we're in segment seek
mode (fixes #340699).