[gimp] app: avoid unnecessary work when all display filters are disabled

[N/A <ell src gnome org>]

commit 6ffa17bd330b4ed428f9b3302efb98d46ef7d17a
Author: Ell <ell_se yahoo com>
Date:   Sun Nov 5 08:57:46 2017 -0500

    app: avoid unnecessary work when all display filters are disabled
    
    Return FALSE from gimp_display_shell_has_filter() when there are
    filters, but they're all disabled, to avoid unnecessary extra
    color conversions during rendering.

 app/display/gimpdisplayshell-filter.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)
---
diff --git a/app/display/gimpdisplayshell-filter.c b/app/display/gimpdisplayshell-filter.c
index bb69b3b..a9c8756 100644
--- a/app/display/gimpdisplayshell-filter.c
+++ b/app/display/gimpdisplayshell-filter.c
@@ -76,7 +76,18 @@ gimp_display_shell_has_filter (GimpDisplayShell *shell)
 {
   g_return_val_if_fail (GIMP_IS_DISPLAY_SHELL (shell), FALSE);
 
-  return shell->filter_stack && shell->filter_stack->filters;
+  if (shell->filter_stack)
+    {
+      GList *iter;
+
+      for (iter = shell->filter_stack->filters; iter; iter = g_list_next (iter))
+        {
+          if (gimp_color_display_get_enabled (GIMP_COLOR_DISPLAY (iter->data)))
+            return TRUE;
+        }
+    }
+
+  return FALSE;
 }
 
 GimpColorDisplayStack *