[gtk/gtk-4-6] gtkscrolledwindow: Do not try to doubly trigger deceleration

[Matthias Clasen <matthiasc src gnome org>]

commit 3764b27babc1cf94f27dfe2079426846d53d0256
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Feb 28 20:27:43 2022 +0100

    gtkscrolledwindow: Do not try to doubly trigger deceleration
    
    This may come from different sources at around the same time, e.g.
    a hold gesture while on overshoot. Avoid doing that if an
    animation is already set.
    
    Fixes: https://gitlab.gnome.org/GNOME/gtk/-/issues/4730

 gtk/gtkscrolledwindow.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index 49be97080c..ee8c2b0ba4 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -1052,7 +1052,8 @@ gtk_scrolled_window_decelerate (GtkScrolledWindow *scrolled_window,
 
   if (priv->x_velocity != 0 || priv->y_velocity != 0 || overshoot)
     {
-      gtk_scrolled_window_start_deceleration (scrolled_window);
+      if (priv->deceleration_id == 0)
+        gtk_scrolled_window_start_deceleration (scrolled_window);
       priv->x_velocity = priv->y_velocity = 0;
     }
 }