[GSS](7.4.z) UNDERTOW-2015 - Undertow AJP listener does not ignore a query parameter that name and value are empty

When a client sends a request with some query parameters which is empty key/value unexpectedly like the following:

http://localhost/example/test.jsp?&foo1=bar1&foo2=bar2

For the above request, ServletRequest#getParameterNames() should return foo1 and foo2.

However, when the request comes through the AJP protocol, URLUtils' QueryStringParser#parse(), which is called from AjpRequestParser, adds an empty key/value param to HttpServerExchange in addition to foo1 and foo2. So, ServletRequest#getParameterNames() returns the different result.

It appears that HttpRequestParser ignores such empty key/value query parameter, so it looks like AJP listener specific issue.