[gnome-control-center] wacom: Fix possible use before set

[Bastien Nocera <hadess src gnome org>]

commit c3c2b23487f7360f2243f2fff15aab0001288330
Author: Bastien Nocera <hadess hadess net>
Date:   Tue Jul 30 16:42:23 2013 +0200

    wacom: Fix possible use before set

 panels/wacom/cc-wacom-button-row.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/panels/wacom/cc-wacom-button-row.c b/panels/wacom/cc-wacom-button-row.c
index 31b531d..78adebf 100644
--- a/panels/wacom/cc-wacom-button-row.c
+++ b/panels/wacom/cc-wacom-button-row.c
@@ -120,6 +120,10 @@ cc_wacom_button_row_update_shortcut (CcWacomButtonRow *row,
 
           g_strfreev (strv);
         }
+      else
+        {
+          shortcut = NULL;
+        }
     }
   else
     shortcut = g_settings_get_string (button->settings, CUSTOM_ACTION_KEY);