[gupnp] Fix build with hardened security flags

[Jens Georg <jensgeorg src gnome org>]

commit 6eba07bd195e0a1199a0fc62d7cc31ec376bc3dd
Author: Andreas Müller <schnitzeltony gmail com>
Date:   Mon May 31 17:44:29 2021 +0200

    Fix build with hardened security flags
    
    | ../gupnp-1.2.6/examples/get-volume.c: In function 'on_introspection':
    | ../gupnp-1.2.6/examples/get-volume.c:53:17: error: format not a string literal and no format arguments 
[-Werror=format-security]
    |    53 |                 g_critical (error->message);
    |       |                 ^~~~~~~~~~
    | ../gupnp-1.2.6/examples/get-volume.c:114:17: error: format not a string literal and no format arguments 
[-Werror=format-security]
    |   114 |                 g_critical (error->message);
    |       |                 ^~~~~~~~~~
    | ../gupnp-1.2.6/examples/get-volume.c: In function 'main':
    | ../gupnp-1.2.6/examples/get-volume.c:150:17: error: format not a string literal and no format arguments 
[-Werror=format-security]
    |   150 |                 g_error (error->message);
    |       |                 ^~~~~~~
    
    Signed-off-by: Andreas Müller <schnitzeltony gmail com>

 examples/get-volume.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/examples/get-volume.c b/examples/get-volume.c
index 4601014..923581c 100644
--- a/examples/get-volume.c
+++ b/examples/get-volume.c
@@ -50,7 +50,7 @@ on_introspection (GObject *object, GAsyncResult *res, gpointer user_data)
                 &error);
 
         if (error != NULL) {
-                g_critical (error->message);
+                g_critical ("%s", error->message);
                 g_clear_error (&error);
         }
 
@@ -111,7 +111,7 @@ on_introspection (GObject *object, GAsyncResult *res, gpointer user_data)
         g_list_free (out_names);
 
         if (error != NULL) {
-                g_critical (error->message);
+                g_critical ("%s", error->message);
                 g_clear_error (&error);
         } else {
                 g_print ("Current volume: %s\n",
@@ -147,7 +147,7 @@ int main(int argc, char *argv[])
         GUPnPContext *context = gupnp_context_new ("wlp3s0", 0, &error);
 
         if (error != NULL) {
-                g_error (error->message);
+                g_error ("%s", error->message);
         }
 
         GUPnPControlPoint *cp = gupnp_control_point_new (context, CONTENT_DIR);