Fix attachment not being re-downloaded even if file is not stored

[Gargron]

Change the behaviour of remotable concern. Previously, it would skip downloading an attachment if the stored remote URL is identical to the new one. Now it would not be skipped if the attachment is not
actually currently stored by Paperclip.

Clean up some code style issues

[saper]

Could this https://discourse.joinmastodon.org/t/media-federation-issue-from-other-instance/2409/8?u=saper be related? Files in /tmp getting removed before they can be processed by Paperclip?

Dec 18 20:53:34 canors_ubuntu bundle[7872]: [paperclip] Link failed with
       No such file or directory @ rb_file_s_link -  
       (/tmp/8d777f385d3dfec8815d20f7496026dc20191218-7872-1inp97p, 
        /tmp/0e5a4502ebd6ef8093a97f30d75321b120191218-7872-jx4qkf); 
        copying link /tmp/8d777f385d3dfec8815d20f7496026dc20191218-7872-1inp97p to    
        /tmp/0e5a4502ebd6ef8093a97f30d75321b120191218-7872-jx4qkf

and

Dec 18 20:53:34 canors_ubuntu bundle[7872]: 
2019-12-18T11:53:34.311Z 7872 TID-gou8367tc 
WARN: Errno::ENOENT: No such file or directory @ rb_sysopen - 
/tmp/8d777f385d3dfec8815d20f7496026dc20191218-7872-1inp97p

(newlines added for readability, full log: https://gist.github.com/Canorus/e5601bfe69a50c7a377e898d93ac223c)

[Gargron]

I find it highly unlikely for this to be the cause. Paperclip is only invoked in the first place by the line send("#{attachment_name}=", StringIO.new(response.body_with_limit(limit))), since this PR would return earlier, no Paperclip methods would be executed.

[saper]

I don't know the exact symptoms of the issue fixed here.

i was wondering whether this could cause or maybe fix the problem reported by the OP. I see we have changed the way we remove temp files... -

Thanks