Dropzone displaying error page html, not error

[sbulen]

Description

I think Dropzone may have an issue when a server-side error is encountered. Instead of displaying the error, it displays the html of the error page served up by the server...

Note, I cannot reproduce this. Sharing in case it looks familiar to someone?

Multiple threads from the support board:
https://www.simplemachines.org/community/index.php?topic=575402.0
https://www.simplemachines.org/community/index.php?topic=575434.0

This exact dropzone issue has been reported before - apparently if there is a server-side error reported this can happen. This thread shows how to trap the error instead of serving up the html:
https://stackoverflow.com/questions/39761736/dropzone-image-upload-error-display-how-to-remove-error

What you see instead (with console window open):

This is the error in the console:

If you click on the link in the console error, this is what you see:

[sbulen]

I have confirmed here that part of the problem is that current_board is undefined...

So, this new logic kicks in:
https://github.com/SimpleMachines/SMF2.1/pull/6301/files

As a result, the URL built to upload the attachment has no board on it, which, I think, is why there is a permissions error on the upload.

The js currently thinks it is being passed an error message to display. But since the problem is bigger & deeper, our fatal error form is presented. An entire page of html, which then gets embedded into the .js error message box where normally a message gets displayed...

[sbulen]

I can reproduce this using the current GitHub code. Just add a regular user & have them try to upload a file.

I cannot reproduce this with RC3. This appears to be due a post-RC3 change.

[sbulen]

Reverting this PR fixes it:
https://github.com/SimpleMachines/SMF2.1/pull/6301/files

@jdarwood007 - could you take a peek?

[smfbigguy]

Taking that code out worked perfect for me.