[glom] ComboBox_Relationship: Fix a typo in a null check.

[Murray Cumming <murrayc src gnome org>]

commit 889f8ae9a6403451a4b00656d5cfa6a778080fa3
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Sep 9 18:36:10 2015 +0200

    ComboBox_Relationship: Fix a typo in a null check.

 glom/mode_design/layout/combobox_relationship.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/glom/mode_design/layout/combobox_relationship.cc 
b/glom/mode_design/layout/combobox_relationship.cc
index 4c2c82a..34a0db4 100644
--- a/glom/mode_design/layout/combobox_relationship.cc
+++ b/glom/mode_design/layout/combobox_relationship.cc
@@ -224,7 +224,7 @@ void ComboBox_Relationship::on_cell_data_title(const Gtk::TreeModel::const_itera
     {
       //related relationship:
       std::shared_ptr<Relationship> parent_relationship = (*iterParent)[m_model_columns.m_relationship];
-      if(relationship)
+      if(parent_relationship)
         m_renderer_title->set_property("text", item_get_title_or_name(parent_relationship) + "::" + 
item_get_title_or_name(relationship));
     }
     else