[gimp] app: treat the layer mask correctly in gimp_layer_get_opacity_at()

[Michael Natterer <mitch src gnome org>]

commit bb43a89ef885d5e46ef1194b40e86cc583dc2c58
Author: Michael Natterer <mitch gimp org>
Date:   Sun May 22 19:53:10 2016 +0200

    app: treat the layer mask correctly in gimp_layer_get_opacity_at()
    
    Only take the mask into account if it is actually applied.

 app/core/gimplayer.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/app/core/gimplayer.c b/app/core/gimplayer.c
index b6856eb..ce88a12 100644
--- a/app/core/gimplayer.c
+++ b/app/core/gimplayer.c
@@ -1235,7 +1235,8 @@ gimp_layer_get_opacity_at (GimpPickable *pickable,
                               GEGL_SAMPLER_NEAREST, GEGL_ABYSS_NONE);
         }
 
-      if (layer->mask)
+      if (gimp_layer_get_mask (layer) &&
+          gimp_layer_get_apply_mask (layer))
         {
           gdouble mask_value;