Re-arrange the checks so that if there is no form parameter, then
immediately and unconditionally delegate to super.getParameterValues().
Or reversely if there is no super.getParameterValues() then return the
form parameter.
So the only remaining case is when combining values present in both.
In that case we'll take both only if a queryString exists.
One extra fix is to not even wrap the request if we did not parse any
form parameters at all which can happen with HttpHiddenMethodFilter.
Issue: SPR-15828, 15835
af83d2332a