basesrc: Flush-stop starts live task in paused
basesrc: Flush-stop starts live task in paused

The flush-stop event should not restart the task for live sources unless
the element is playing. This was breaking seeks in pause with the rtpsrc.

https://bugzilla.gnome.org/show_bug.cgi?id=635701

jpxiong/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,krichter722/gstreamer,mparis/gstreamer,centricular/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,mparis/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,mparis/gstreamer,krichter722/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,mparis/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,jpxiong/gstreamer,centricular/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer