[gimp] Bug 793669 - histogram-related bug report.

[Jehan Pagès <jehanp src gnome org>]

commit 35352519790ab983b2a4f7874c07a946d0a06151
Author: Jehan <jehan girinstud io>
Date:   Wed Feb 21 16:45:13 2018 +0100

    Bug 793669 - histogram-related bug report.
    
    When the histogram is freed, we need to set valid to FALSE, in order to
    force recreation as soon as needed. Otherwise we may hit some race
    condition of trying to work with a NULL histogram. For instance this
    happened when starting painting fast enough after switching the active
    image.

 app/widgets/gimphistogrameditor.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/app/widgets/gimphistogrameditor.c b/app/widgets/gimphistogrameditor.c
index 277c1bc..d771189 100644
--- a/app/widgets/gimphistogrameditor.c
+++ b/app/widgets/gimphistogrameditor.c
@@ -252,6 +252,7 @@ gimp_histogram_editor_set_property (GObject      *object,
       if (editor->histogram)
         {
           g_clear_object (&editor->histogram);
+          editor->valid = FALSE;
           gimp_histogram_view_set_histogram (view, NULL);
         }
 
@@ -349,6 +350,7 @@ gimp_histogram_editor_set_image (GimpImageEditor *image_editor,
       if (editor->histogram)
         {
           g_clear_object (&editor->histogram);
+          editor->valid = FALSE;
           gimp_histogram_view_set_histogram (view, NULL);
         }
 
@@ -394,6 +396,7 @@ gimp_histogram_editor_layer_changed (GimpImage           *image,
       if (editor->histogram)
         {
           g_clear_object (&editor->histogram);
+          editor->valid = FALSE;
           gimp_histogram_view_set_histogram (view, NULL);
         }