ext/gio/: Use async variants of the close stream functions to prevent blocking for a long time there and add some mor...

Original commit message from CVS:
* ext/gio/gstgiobasesink.c: (close_stream_cb),
(gst_gio_base_sink_stop), (gst_gio_base_sink_event),
(gst_gio_base_sink_render), (gst_gio_base_sink_set_stream):
* ext/gio/gstgiobasesrc.c: (close_stream_cb),
(gst_gio_base_src_stop), (gst_gio_base_src_create),
(gst_gio_base_src_set_stream):
Use async variants of the close stream functions to prevent blocking
for a long time there and add some more sanity checks for a correct
stream.