Issue #1141 - When Accept header or Accept-Charset header has invalid QualityFactor we throw.

Issue #1141 
Fix: Imitating the same behavior as it is in WebApi. We ignore the entire header even if one part of it is invalid.
```C#
if (!MediaTypeWithQualityHeaderValue.TryParse(item, out parsedAcceptHeader))
{
    return null;
}
```