Fix preview for textual inversion training

        assert log_directory, "Log directory is empty"

def train_embedding(id_task, embedding_name, learn_rate, batch_size, gradient_step, data_root, log_directory, training_width, training_height, varsize, steps, clip_grad_mode, clip_grad_value, shuffle_tags, tag_drop_out, latent_sampling_method, use_weight, create_image_every, save_embedding_every, template_filename, save_image_with_stored_embedding, preview_from_txt2img, preview_prompt, preview_negative_prompt, preview_steps, preview_sampler_index, preview_cfg_scale, preview_seed, preview_width, preview_height):

def train_embedding(id_task, embedding_name, learn_rate, batch_size, gradient_step, data_root, log_directory, training_width, training_height, varsize, steps, clip_grad_mode, clip_grad_value, shuffle_tags, tag_drop_out, latent_sampling_method, use_weight, create_image_every, save_embedding_every, template_filename, save_image_with_stored_embedding, preview_from_txt2img, preview_prompt, preview_negative_prompt, preview_steps, preview_sampler_name, preview_cfg_scale, preview_seed, preview_width, preview_height):

    from modules import processing

    save_embedding_every = save_embedding_every or 0

                        p.prompt = preview_prompt

                        p.negative_prompt = preview_negative_prompt

                        p.steps = preview_steps

                        p.sampler_name = sd_samplers.samplers[preview_sampler_index].name

                        p.sampler_name = sd_samplers.samplers_map[preview_sampler_name.lower()]

                        p.cfg_scale = preview_cfg_scale

                        p.seed = preview_seed

                        p.width = preview_width