[Bug] file extension not saved

[yo-gen]

Bug report:

• Expected Behavior:
  If you are willing to add a specific filename to your attachment, or send in a specific content type for your file, you can use data: to attach the base64 data and specify your filename:, content_type: and/or identify: hash keys
• Actual Behavior:
  Identify Hash key doesn't identify the file extension automatically. Infact the extension is not recognized when uploading a valid base 64 URI.
• Steps to Reproduce:
  1. Create a model with a field for attachment
  2. Pass a base64 data URI to file attachment and save it. Pass only the base 64 string in data, without filename and content_type parameters.
  3. Check the filename and it does not have an extension. Filename will have the random generated time string but will lose the extension.
• Create an executable test case: use the bug_report_template.rb as a starting point.
  You can execute it by running ruby the_bug_report_filename.rb
• Version of the repo:
• Ruby and Rails Version:
• Rails Stacktrace: this can be found in the log/development.log or log/test.log, if this is applicable.

I think a way for this might be to identify the extension from the file content_type using:

require 'rack/mime'
extension = Rack::Mime::MIME_TYPES.invert[attachment[:content_type]]
filename += extension