Accidental infinite loop

[cholcombe973]

I'm not sure this is worth a bug report but I think I'll post this anyways just for anyone else that runs into it. I wrote my own little multipart form generator and I forgot to include 2 extra dashes in the boundary field. This causes the form-data crate to spin off into an infinite loop when trying to parse the form. The fix for this might be to just reject it as an invalid form.