default to ignore existing captions

modules/ui.py

@@ -1234,7 +1234,7 @@ def create_ui(wrap_gradio_gpu_call):
                     process_dst = gr.Textbox(label='Destination directory')
                     process_width = gr.Slider(minimum=64, maximum=2048, step=64, label="Width", value=512)
                     process_height = gr.Slider(minimum=64, maximum=2048, step=64, label="Height", value=512)
-                    preprocess_txt_action = gr.Dropdown(label='Existing Caption txt Action', choices=['ignore', 'copy', 'prepend', 'append'])
+                    preprocess_txt_action = gr.Dropdown(label='Existing Caption txt Action', value="ignore", choices=["ignore", "copy", "prepend", "append"])
 
                     with gr.Row():
                         process_flip = gr.Checkbox(label='Create flipped copies')