func (a *Args) QueryString() []byte {
	a.buf = a.AppendBytes(a.buf[:0])
	return a.buf
}
func (a *Args) QueryString() []byte {
	a.buf = a.AppendBytes(a.buf[:0])
	return a.buf
}
// QueryString returns query string for the args.
//
// The returned value is valid until the next call to Args methods.