When user using model_name.png as a preview image, textural_inversion.py still treat it as an embeding, and didn't handle its error, just let python throw out an None type error like following:
```bash
File "D:\Work\Dev\AI\stable-diffusion-webui\modules\textual_inversion\textual_inversion.py", line 155, in load_from_file
name = data.get('name', name)
AttributeError: 'NoneType' object has no attribute 'get'
```
With just a simple `if data:` checking as following, there will be no error, breaks nothing, and now this module can works fine with user's preview images.
Old code:
```python
data = extract_image_data_embed(embed_image)
name = data.get('name', name)
```
New code:
```python
data = extract_image_data_embed(embed_image)
if data:
name = data.get('name', name)
else:
# if data is None, means this is not an embeding, just a preview image
return
```
Also, since there is no more errors on textual inversion module, from now on, extra network can set "model_name.png" as preview image for embedings.
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