Status code and message improvement when validate presentation proof with empty body - Negative Test

Summary:

When requesting presentation proof with empty body the status code is 500 "Internal Server Error".

Expected:

HTTP/1.1 400 Bad Request
{
    ...
    "message": "missing required payload"
}

Actual:

HTTP/1.1 500 Internal Server Error
{
    ...
    "message": "verifiable presentation is not valid:\n- (root): @context is required\n- (root): type is required\n"
}