client: Don't provide statistics if vpnclient object is unavailable

Querying the statistics object too early before the vpnclient object has
been started (can happen in 2FA situations) will cause the client
process to segfault as vpnclient is nullptr.

Signed-off-by: David Sommerseth <davids@openvpn.net>

src/client/openvpn3-service-client.cpp

@@ -634,10 +634,13 @@ class BackendClientObject : public DBusObject,
                 // Returns an array of a string (description) and an int64
                 // containing the statistics value.
                 GVariantBuilder *b = g_variant_builder_new(G_VARIANT_TYPE("a{sx}"));
-                for (auto& sd : vpnclient->GetStats())
+                if (vpnclient)
                 {
-                    g_variant_builder_add (b, "{sx}",
-                                           sd.key.c_str(), sd.value);
+                    for (auto& sd : vpnclient->GetStats())
+                    {
+                        g_variant_builder_add (b, "{sx}",
+                                               sd.key.c_str(), sd.value);
+                    }
                 }
                 GVariant *ret = g_variant_builder_end(b);
                 g_variant_builder_unref(b);