network: fix crash when adding cellular connection (#329)

As GTK is loaded first, while libNMA is loaded later with the network panel
extension, the GtkBuilder for the wizard GUI doesn't know the libNMA types.

To fix that, we need to ensure the registration of these types.

Fixes: #225, #246

panels/network/network-dialogs.c

@@ -23,6 +23,7 @@
 #include <NetworkManager.h>
 #include <nma-wifi-dialog.h>
 #include <nma-mobile-wizard.h>
+#include <nma-mobile-providers.h>
 
 #include "network-dialogs.h"
 
@@ -472,6 +473,10 @@ cc_network_panel_connect_to_3g_network (GtkWidget        *toplevel,
         closure->client = g_object_ref (client);
         closure->device = g_object_ref (device);
 
+        g_type_ensure (NMA_TYPE_COUNTRY_INFO);
+        g_type_ensure (NMA_TYPE_MOBILE_ACCESS_METHOD);
+        g_type_ensure (NMA_TYPE_MOBILE_PROVIDER);
+
 	caps = nm_device_modem_get_current_capabilities (NM_DEVICE_MODEM (device));
 	if (caps & NM_DEVICE_MODEM_CAPABILITY_GSM_UMTS) {
                 wizard = nma_mobile_wizard_new (GTK_WINDOW (toplevel), NULL, NM_DEVICE_MODEM_CAPABILITY_GSM_UMTS, FALSE,