gst-player: fix bug with changing playback direction

gst-player: fix bug with changing playback direction

Fix gst_event_new_seek call in gst-libs/gst/player/gstplayer.c

If rate >= 0.0, then previous code doesn't set end of segment. So, the end of segment
will be in place where previous seek put it. This is not neccesary end of media file
(in case of reverse playback). So if we play video backward for some time and then
switched to forward playing, we will get EOS somewhere in the middle of media file.
This commit always sets end of segment, thus fixing this bug