[glib/wip/ernestask/gcc-9-null-directive-argument] gdbus: Avoid printing null strings

[Ernestas Kulik <ernestask src gnome org>]

commit 566e1d61a500267c7849ad0b2552feec9c9a29a6
Author: Ernestas Kulik <ekulik redhat com>
Date:   Tue Jan 29 09:50:46 2019 +0100

    gdbus: Avoid printing null strings
    
    This mostly affects the 2.56 branch, but, given that GCC 9 is being
    stricter about passing null string pointers to printf-like functions, it
    might make sense to proactively fix such calls.
    
    gdbusauth.c: In function '_g_dbus_auth_run_server':
    gdbusauth.c:1302:11: error: '%s' directive argument is null
    [-Werror=format-overflow=]
     1302 |           debug_print ("SERVER: WaitingForBegin, read '%s'",
     line);
           |
    
    gdbusmessage.c: In function ‘g_dbus_message_to_blob’:
    gdbusmessage.c:2730:30: error: ‘%s’ directive argument is null [-Werror=format-overflow=]
     2730 |       tupled_signature_str = g_strdup_printf ("(%s)", signature_str);
          |

 gio/gdbusauth.c    | 2 +-
 gio/gdbusmessage.c | 5 ++---
 2 files changed, 3 insertions(+), 4 deletions(-)
---
diff --git a/gio/gdbusauth.c b/gio/gdbusauth.c
index 1f8ea8057..752ec23fc 100644
--- a/gio/gdbusauth.c
+++ b/gio/gdbusauth.c
@@ -1272,9 +1272,9 @@ _g_dbus_auth_run_server (GDBusAuth              *auth,
                                                     &line_length,
                                                     cancellable,
                                                     error);
-          debug_print ("SERVER: WaitingForBegin, read '%s'", line);
           if (line == NULL)
             goto out;
+          debug_print ("SERVER: WaitingForBegin, read '%s'", line);
           if (g_strcmp0 (line, "BEGIN") == 0)
             {
               /* YAY, done! */
diff --git a/gio/gdbusmessage.c b/gio/gdbusmessage.c
index 3221b925d..3a1a1f9e9 100644
--- a/gio/gdbusmessage.c
+++ b/gio/gdbusmessage.c
@@ -2731,7 +2731,6 @@ g_dbus_message_to_blob (GDBusMessage          *message,
   if (message->body != NULL)
     {
       gchar *tupled_signature_str;
-      tupled_signature_str = g_strdup_printf ("(%s)", signature_str);
       if (signature == NULL)
         {
           g_set_error (error,
@@ -2739,10 +2738,10 @@ g_dbus_message_to_blob (GDBusMessage          *message,
                        G_IO_ERROR_INVALID_ARGUMENT,
                        _("Message body has signature “%s” but there is no signature header"),
                        signature_str);
-          g_free (tupled_signature_str);
           goto out;
         }
-      else if (g_strcmp0 (tupled_signature_str, g_variant_get_type_string (message->body)) != 0)
+      tupled_signature_str = g_strdup_printf ("(%s)", signature_str);
+      if (g_strcmp0 (tupled_signature_str, g_variant_get_type_string (message->body)) != 0)
         {
           g_set_error (error,
                        G_IO_ERROR,