[gimp/gimp-2-10] app: in GimpPanedBox, don't accept drag contexts with unsupported targets

[Ell <ell src gnome org>]

commit b5353eb2ebb59cc0cd1fa875e26984f7edf7a8cb
Author: Ell <ell_se yahoo com>
Date:   Mon May 18 18:14:37 2020 +0300

    app: in GimpPanedBox, don't accept drag contexts with unsupported targets
    
    ... to avoid highlighting the droppable areas during darg.
    
    (cherry picked from commit e38010b2d1d9a40b5d42c2986bf356565a5465b6)

 app/widgets/gimppanedbox.c | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/app/widgets/gimppanedbox.c b/app/widgets/gimppanedbox.c
index ba04b9a1cf..15e8b542fe 100644
--- a/app/widgets/gimppanedbox.c
+++ b/app/widgets/gimppanedbox.c
@@ -296,6 +296,12 @@ gimp_paned_box_get_handle_drag (GimpPanedBox   *paned_box,
       return FALSE;
     }
 
+  if (gtk_drag_dest_find_target (GTK_WIDGET (paned_box), context, NULL) ==
+      GDK_NONE)
+    {
+      return FALSE;
+    }
+
   gtk_widget_get_allocation (GTK_WIDGET (paned_box), &allocation);
 
   /* See if we're at the edge of the dock If there are no dockables,