Fix potential crashes in case of a bad parameter.

In both function, if type parameter is NULL, the call to
resource_type_match will crash as this function call strcmp on type
without any check.

https://bugzilla.gnome.org/show_bug.cgi?id=704094

libgupnp/gupnp-device-info.c

@@ -1117,6 +1117,7 @@ gupnp_device_info_get_device (GUPnPDeviceInfo *info,
         xmlNode *element;
 
         g_return_val_if_fail (GUPNP_IS_DEVICE_INFO (info), NULL);
+        g_return_val_if_fail (type != NULL, NULL);
 
         class = GUPNP_DEVICE_INFO_GET_CLASS (info);
 
@@ -1271,6 +1272,7 @@ gupnp_device_info_get_service (GUPnPDeviceInfo *info,
         xmlNode *element;
 
         g_return_val_if_fail (GUPNP_IS_DEVICE_INFO (info), NULL);
+        g_return_val_if_fail (type != NULL, NULL);
 
         class = GUPNP_DEVICE_INFO_GET_CLASS (info);