Bug fix for part deep-copy

- Don't copy an image if an image doesn't exist

InvenTree/part/models.py

@@ -574,6 +574,7 @@ class Part(models.Model):
 
         # Copy the part image
         if kwargs.get('image', True):
+            if other.image:
                 image_file = ContentFile(other.image.read())
                 image_file.name = rename_part_image(self, 'test.png')