core: Apply filters without GUIs as NDE contextually

If someone applies a GEGL filter without a GUI like Invert
on top of a layer with existing filters, they likely expect the
filter to apply on top. Currently, we always apply filters
without GUIs destructively, which can be confusing if you
have a filter that covers the entire layer like Simplex Noise.

This patch adds a check if the layer has any visible filters,
and if so, the filter is committed non-destructively. If all
filters are currently invisible, the non-GUI filter is still
applied destructively as in 5e3047c7.

app/core/gimpdrawable-operation.c

@@ -63,6 +63,7 @@ gimp_drawable_apply_operation_with_config (GimpDrawable *drawable,
 {
   GimpDrawableFilter *filter;
   GimpContainer      *filter_stack;
+  gboolean            is_non_destructive = FALSE;
 
   g_return_if_fail (GIMP_IS_DRAWABLE (drawable));
   g_return_if_fail (gimp_item_is_attached (GIMP_ITEM (drawable)));
@@ -93,14 +94,16 @@ gimp_drawable_apply_operation_with_config (GimpDrawable *drawable,
 
   gimp_drawable_filter_apply  (filter, NULL);
 
+  is_non_destructive = gimp_drawable_has_visible_filters (drawable);
+
   /* For destructive filters, we want them to apply directly on the
    * drawable rather than merge down onto existing NDE filters */
   filter_stack = gimp_drawable_get_filters (drawable);
-  if (filter_stack)
+  if (filter_stack && ! is_non_destructive)
     gimp_container_reorder (filter_stack, GIMP_OBJECT (filter),
                             gimp_container_get_n_children (filter_stack) - 1);
 
-  gimp_drawable_filter_commit (filter, FALSE, progress, TRUE);
+  gimp_drawable_filter_commit (filter, is_non_destructive, progress, TRUE);
 
   g_object_unref (filter);