video-texture: introduce change_uri internal state
video-texture: introduce change_uri internal state

This allows to manage the set_progress call right after/before a set_uri
call.

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