Do not return early if both content-type and content-length is specified.

Calling putFile with both content-type and content-length headers would result in the upload never starting, and the callback never called.

I believe this was a bug introduced in 15e22278cc31.
Merge remote-tracking branch 'marcuswestin/master' into future
Added Content-Type and Content-Lenght to S3 PUT foo.txt as regression for #78.