ext/gio/: Some minor cleanup and allow setting the location only when the element is not playing or paused.

Original commit message from CVS:
* ext/gio/gstgiosink.c: (gst_gio_sink_base_init),
(gst_gio_sink_set_property), (gst_gio_sink_render):
* ext/gio/gstgiosrc.c: (gst_gio_src_base_init),
(gst_gio_src_set_property):
Some minor cleanup and allow setting the location only when the
element is not playing or paused.