[gtk/wip/baedert/radial-gradient] scrolledwindow: Ignore captured motion events if no child is set

[Timm Bäder <baedert src gnome org>]

commit 1d371db8d8e96d87a54c6d45f99c255a8e4a3061
Author: Timm Bäder <mail baedert org>
Date:   Sat Sep 19 08:44:58 2020 +0200

    scrolledwindow: Ignore captured motion events if no child is set
    
    Fixes #3173

 gtk/gtkscrolledwindow.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index fbc03039e4..2e24b21b38 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -1250,6 +1250,9 @@ captured_motion (GtkEventController *controller,
   if (!priv->use_indicators)
     return;
 
+  if (!priv->child)
+    return;
+
   target = gtk_event_controller_get_target (controller);
   state = gtk_event_controller_get_current_event_state (controller);
   event = gtk_event_controller_get_current_event (controller);