[gnome-boxes] vm-configurator: Add a sanity check

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit f18da82afbaebfdd44a56ccd5fc7323f4f7de833
Author: Zeeshan Ali (Khattak) <zeeshanak gnome org>
Date:   Wed Jun 5 04:19:15 2013 +0300

    vm-configurator: Add a sanity check
    
    https://bugzilla.gnome.org/show_bug.cgi?id=690757

 src/vm-configurator.vala |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/vm-configurator.vala b/src/vm-configurator.vala
index 8e8cc67..fe14e39 100644
--- a/src/vm-configurator.vala
+++ b/src/vm-configurator.vala
@@ -340,6 +340,7 @@ private class Boxes.VMConfigurator {
                                            InstallerMedia? install_media,
                                            uint num_reboots = 0,
                                            bool installed = false) {
+        return_if_fail (install_media != null || installed);
         string custom_xml;
 
         if (installed)