event: Don't allow invalid SELECT_STREAMS event creation
event: Don't allow invalid SELECT_STREAMS event creation

Asking to select no streams makes no sense and can create various
issues.

If one doesn't one any stream it should deactivate (or not use) the
element in question.

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer