[gimp] app: put back two lines that got lost in earlier GTK+ 3.0 porting

[Michael Natterer <mitch src gnome org>]

commit 960b530d03a4c9b50c951c52b3835da1860aa536
Author: Michael Natterer <mitch gimp org>
Date:   Wed May 2 21:20:19 2018 +0200

    app: put back two lines that got lost in earlier GTK+ 3.0 porting

 app/widgets/gimpspinscale.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/app/widgets/gimpspinscale.c b/app/widgets/gimpspinscale.c
index 484eaa9..6e12607 100644
--- a/app/widgets/gimpspinscale.c
+++ b/app/widgets/gimpspinscale.c
@@ -804,6 +804,9 @@ gimp_spin_scale_button_press (GtkWidget      *widget,
       private->start_x = x;
       private->start_value = gtk_adjustment_get_value (gtk_spin_button_get_adjustment (GTK_SPIN_BUTTON 
(widget)));
 
+      private->start_pointer_x = floor (event->x_root);
+      private->start_pointer_y = floor (event->y_root);
+
       return TRUE;
 
     default: