Handle possible corrupted image when using `image_field` option.

**Python version**
3.8

**Django version**
3.2

**Package version**
0.7.2

**Current behavior (bug description)**
Using `image_field`, if the uploaded image is corrupted a `UnidentifiedImageError` is raised and the whole model save is interrupted.

**Expected behavior**
Handle the error, extract no color and continue saving model correctly.
