Ensure request.POST always raises EOFError on bad input

Before this fix, if you had a bad multipart request, request.POST would only raise EOFError the first time it was called, and would then return nil on subsequent invocations.  This would typically result in the cryptic "can't convert nil into Hash" as a result of calling request.params
Merge pull request #561 from jdelStrother/eoferror

Ensure request.POST always raises EOFError on bad input