[glib/wip/hadess/check-g_variant_get-args] gvariant: Add guard to g_variant_get()

[Bastien Nocera <hadess src gnome org>]

commit 43d3d492349f0a540f6f4eaa800697449f1a2fdb
Author: Bastien Nocera <hadess hadess net>
Date:   Wed Dec 4 18:36:40 2019 +0100

    gvariant: Add guard to g_variant_get()
    
    Even if g_variant_get_va(), which we eventually call, checks on the
    validity of the value argument, check it early to avoid surprises, such
    as this intermittent FreeBSD test failure:
    (/var/tmp/gitlab_runner/builds/3fe11159/0/GNOME/glib/_build/gio/tests/gdbus-connection:65788): 
GLib-CRITICAL **: 15:13:25.670: g_variant_get_va: assertion 'value != NULL' failed

 glib/gvariant.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/glib/gvariant.c b/glib/gvariant.c
index d7ec8dc70..ee1a9c020 100644
--- a/glib/gvariant.c
+++ b/glib/gvariant.c
@@ -5434,6 +5434,7 @@ g_variant_get (GVariant    *value,
 {
   va_list ap;
 
+  g_return_if_fail (value != NULL);
   g_return_if_fail (valid_format_string (format_string, TRUE, value));
 
   /* if any direct-pointer-access formats are in use, flatten first */