[gnome-boxes] wizard: Only show cutomize button for single machine

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit 0d5180a9b71613fb640cfa327f1f07da5a20126e
Author: Zeeshan Ali (Khattak) <zeeshanak gnome org>
Date:   Mon Nov 18 23:53:34 2013 +0000

    wizard: Only show cutomize button for single machine
    
    Currently customization during wizard is only supported when
    creating/adding a single machine so lets not present a non-working
    option to user.

 src/wizard.vala |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)
---
diff --git a/src/wizard.vala b/src/wizard.vala
index f04e7dd..04eeb72 100644
--- a/src/wizard.vala
+++ b/src/wizard.vala
@@ -463,10 +463,11 @@ private class Boxes.Wizard: Boxes.UI {
             nokvm_box.visible = (libvirt_machine.domain_config.get_virt_type () != 
GVirConfig.DomainVirtType.KVM);
         }
 
-        summary.append_customize_button (() => {
-            // Selecting an item in UIState.WIZARD implies changing state to UIState.PROPERTIES
-            App.app.select_item (machine);
-        });
+        if (machine != null)
+            summary.append_customize_button (() => {
+                // Selecting an item in UIState.WIZARD implies changing state to UIState.PROPERTIES
+                App.app.select_item (machine);
+            });
 
         return true;
     }