[gimp] libgimpwidgets: show help buttons in dialogs again

[Michael Natterer <mitch src gnome org>]

commit b119fc995a00e9e029ded11bbf19389477983659
Author: Michael Natterer <mitch gimp org>
Date:   Sun Feb 12 16:31:23 2017 +0100

    libgimpwidgets: show help buttons in dialogs again
    
    GimpDialog's "help-id" property didn't have G_PARAM_CONSTRUCT.
    
    Broken since commit a94030052521e481cfe996044947c13b4e5c0276.

 libgimpwidgets/gimpdialog.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/libgimpwidgets/gimpdialog.c b/libgimpwidgets/gimpdialog.c
index af652a8..d31deb3 100644
--- a/libgimpwidgets/gimpdialog.c
+++ b/libgimpwidgets/gimpdialog.c
@@ -131,7 +131,8 @@ gimp_dialog_class_init (GimpDialogClass *klass)
   g_object_class_install_property (object_class, PROP_HELP_ID,
                                    g_param_spec_string ("help-id", NULL, NULL,
                                                         NULL,
-                                                        GIMP_PARAM_READWRITE));
+                                                        GIMP_PARAM_READWRITE |
+                                                        G_PARAM_CONSTRUCT));
 
   /**
    * GimpDialog:parent: