Re: [libvirt] [libvirt-glib 1/4] gobject: don't try to use pool's volumes before a successful refresh

gvir_storage_pool_refresh must be called and must be successful before trying to use gvir_storage_pool_get_volume, gvir_storage_pool_get_volumes and gvir_storage_pool_create_volume. As the storage pool refresh can fail for reasons external to libvirt/libvirt-gobject, the library user should check _refresh errors. This commit outputs runtime warnings when these functions are called and GVirObjectStoragePool::priv::volumes is NULL.