[glib] win32: silence build warning

[Matthias Clasen <matthiasc src gnome org>]

commit a8f58fcfec121241be7890f5b340e139f39fd125
Author: Marc-André Lureau <marcandre lureau gmail com>
Date:   Wed Nov 6 13:57:07 2013 +0100

    win32: silence build warning
    
    gdbusauthmechanismexternal.c: In function 'mechanism_client_initiate':
    gdbusauthmechanismexternal.c:355:3: warning: 'initial_response' may be
    used uninitialized in this function [-Wmaybe-uninitialized]
       return initial_response;
       ^
    gdbusauthmechanismexternal.c:332:10: note: 'initial_response' was
    declared here
    
    https://bugzilla.gnome.org/show_bug.cgi?id=711547

 gio/gdbusauthmechanismexternal.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gio/gdbusauthmechanismexternal.c b/gio/gdbusauthmechanismexternal.c
index 38a2f65..f0bcfc3 100644
--- a/gio/gdbusauthmechanismexternal.c
+++ b/gio/gdbusauthmechanismexternal.c
@@ -325,7 +325,7 @@ mechanism_client_initiate (GDBusAuthMechanism   *mechanism,
                            gsize                *out_initial_response_len)
 {
   GDBusAuthMechanismExternal *m = G_DBUS_AUTH_MECHANISM_EXTERNAL (mechanism);
-  gchar *initial_response;
+  gchar *initial_response = NULL;
   GCredentials *credentials;
 
   g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_EXTERNAL (mechanism), NULL);