Skips NPE when a multipart could not be parsed

[sickmartian]

Recording the body instead.

This can happen when content of the multipart is not a file, so there is no header with content disposition giving it a filename. E.g. an OData $batch request.

Wiremock is currently failing the request, giving a 500 back because of the NPE, even when proxying when we got proper data back.

edit went a bit further on the library and saw what was going on, I assumed the lib I was using bad generating the request wrong and hence couldn't be parsed, but really wiremock assumes is going to be files whose parsing will work, not a bad assumption but it doesn't fit certain cases and the NPE is bad.

[sickmartian]

Might be related to #702 although the description says valid json or xml, this might be a more general case.

[tomakehurst]

Thanks!