Reset remote_url field

[cristi-badila]

Hello, I just started using your gem recently and it fits perfectly with what i was trying to accomplish on a project but I encountered the following small issue:
I have a form for a model which has some validation rules on it and a paperclip attachment. I then try to show the form for a model instance that has the paperclip attachment's remote_url attribute pre-populated with an image url. When trying to submit the form if the data from the form is valid, everything is ok and the image is saved; however if the validation rules are broken the remote_url attribute is now empty and I would have to do some weird stuff to get it back again. I tracked down this behavior to line 44 in the remote.rb file which looks like this:

      record.send(:"#{name}_remote_url=", nil) # Reset!

It's obvious that somebody thought that it was required to reset the field, but I don't understand why. Is there any reason for this behavior or can it simply be removed? Thanks for the nice work!

Edit:
I tried forking the repository an removing the line myself and I can see that some specs fail by going into a stack overflow but I don't quite understand why. Can you maybe share some light on why this is required?

Second edit:
Looking at the code more carefully I realized that on line 45 another validation sequence is triggered and if the attribute would still be present, an infinite recursion would occur. Still would like to find a way around this so I'm gonna poke around some more.

Last edit:
Fixed this for myself by using an extra instance variable to track if the original attribute was updated. If you consider this is ok I can make a pull request.