[gthumb] image viewer: added missing attribute when creating the gdk window

[Paolo Bacchilega <paobac src gnome org>]

commit 3d30e4c2e1c4e4c27ab60a3f1e04648c722d5c29
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sat Jan 5 16:19:11 2019 +0100

    image viewer: added missing attribute when creating the gdk window

 gthumb/gth-image-viewer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gthumb/gth-image-viewer.c b/gthumb/gth-image-viewer.c
index 1f4b6f1d..97214a63 100644
--- a/gthumb/gth-image-viewer.c
+++ b/gthumb/gth-image-viewer.c
@@ -443,7 +443,7 @@ gth_image_viewer_realize (GtkWidget *widget)
                                  | GDK_BUTTON_MOTION_MASK
                                  | GDK_SCROLL_MASK
                                  | GDK_STRUCTURE_MASK);
-       attributes_mask = GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL;
+       attributes_mask = GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL | GDK_WA_WMCLASS;
        window = gdk_window_new (gtk_widget_get_parent_window (widget),
                                 &attributes,
                                 attributes_mask);