video-texture: Don't forget to reset the subtitle URI with new media
video-texture: Don't forget to reset the subtitle URI with new media

We did not reset the URI of subtitles when changing media, which lead to
still playing the auto-detected subtitles with the next media.

ystreet/clutter-gst,lubosz/clutter-gst,skinkie/clutter-gst,lubosz/clutter-gst,ystreet/clutter-gst,skinkie/clutter-gst,lubosz/clutter-gst,GNOME/clutter-gst,GNOME/clutter-gst,GNOME/clutter-gst,ystreet/clutter-gst,skinkie/clutter-gst,ystreet/clutter-gst,GNOME/clutter-gst