gst: Ensure gst_value is initialised before gst_tag
gst: Ensure gst_value is initialised before gst_tag

Otherwise GST_TYPE_FRACTION will work correctly in tags.

https://bugzilla.gnome.org/show_bug.cgi?id=753922

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