Prevent file name conflicts due to misconfiguration

[dacook]

Is your feature request related to a problem? Please describe.
I just fixed a problem caused by a misconfiguration with file path. Multiple styles were being generated (:original plus one custom one), but :style wasn't present in the path setting, so a filename conflict occurred.
This resulted in file uploads to a cloud service failing at first (due to a 404 from second delete), then succeeding on second try (no delete request made). It took a long time to figure out why it was "intermittently" failing!!!

Describe the solution you'd like
If there is more than one style (including :original), I think :style should be a required element in the path. Can this be validated upon initialisation?

Describe alternatives you've considered
Alternatively we could update the documentation to point this out
Actually, the path variables and :original style should be more documented anyway.

Additional context
Example configuration that was failing:

has_attached_file :image, path: "images/products/:id_:updated_at.:extension",# <-- no :style
                          default_style: :normal,
                          styles: { 
                            normal: { # <-- new style defined, without realising that :original also exists by default
                              geometry: '600x600#',
                              format: 'jpg',
                              quality: 80
                            }
                          }

Dev log from first try:

[paperclip] deleting images/products/3855_1637107719.jpg
[paperclip] deleting images/products/3855_1637107719.jpg
   (1.9ms)  ROLLBACK