[gimp] app: don't invalidate layer when invalidating its backdrop

[N/A <ell src gnome org>]

commit dd8e2e9b5eaf493ff94f5b0e3407cad83c29bc9c
Author: Ell <ell_se yahoo com>
Date:   Fri May 12 15:51:36 2017 -0400

    app: don't invalidate layer when invalidating its backdrop
    
    Harmless, but unnecessary.

 app/core/gimplayerstack.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/app/core/gimplayerstack.c b/app/core/gimplayerstack.c
index 7011bc7..e45138d 100644
--- a/app/core/gimplayerstack.c
+++ b/app/core/gimplayerstack.c
@@ -185,7 +185,7 @@ gimp_layer_stack_update_backdrop (GimpLayerStack *stack,
       index = gimp_container_get_child_index (GIMP_CONTAINER (stack),
                                               GIMP_OBJECT (layer));
 
-      gimp_layer_stack_update_range (stack, index, -1);
+      gimp_layer_stack_update_range (stack, index + 1, -1);
     }
 }