gtkkineticscroll: Do not reset velocity after stop()

We may want to fetch the last velocity obtained, even though we
preemptively called stop() on a kinetic scroll helper. Keep this
velocity so it can be queried later on.

gtk/gtkkineticscrolling.c

@@ -254,6 +254,5 @@ gtk_kinetic_scrolling_stop (GtkKineticScrolling *data)
     {
       data->phase = GTK_KINETIC_SCROLLING_PHASE_FINISHED;
       data->position = round (data->position);
-      data->velocity = 0;
     }
 }