[evolution] Avoid minor occasional runtime warning

[Milan Crha <mcrha src gnome org>]

commit bcf6723d073c88b24e69a7939bb2a994eb472402
Author: Milan Crha <mcrha redhat com>
Date:   Thu Apr 28 15:37:31 2016 +0200

    Avoid minor occasional runtime warning

 e-util/gal-a11y-e-cell-tree.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/e-util/gal-a11y-e-cell-tree.c b/e-util/gal-a11y-e-cell-tree.c
index ce32ed3..1b20aed 100644
--- a/e-util/gal-a11y-e-cell-tree.c
+++ b/e-util/gal-a11y-e-cell-tree.c
@@ -93,9 +93,11 @@ ectr_subcell_weak_ref (GalA11yECellTree *a11y,
        if (subcell_a11y && subcell_view && subcell_view->kill_view_cb_data)
            subcell_view->kill_view_cb_data = g_list_remove (subcell_view->kill_view_cb_data, subcell_a11y);
 
-       g_signal_handler_disconnect (
-               GAL_A11Y_E_CELL (a11y)->item->table_model,
-               a11y->model_row_changed_id);
+       if (GAL_A11Y_E_CELL (a11y)->item && GAL_A11Y_E_CELL (a11y)->item->table_model) {
+               g_signal_handler_disconnect (
+                       GAL_A11Y_E_CELL (a11y)->item->table_model,
+                       a11y->model_row_changed_id);
+       }
        g_object_unref (a11y);
 }