make HTTPAuthenticationParams::parse() add value on end of string

There is a bug in `Poco::Net::HTTPAuthenticationParams` parser. It doesn't add parameter to the name-value collection if the parameters value is unquoted and it's at the end of the input string. E.g., parameter `nc` will not be in the resulting name-value collection:
```
username="xyz", nc=00000001
```
This commit fixes that.