fix required GET args being present not triggering a 400 when no GET args were passed at all

SimpleHttpServer/HttpServer.cs

@@ -255,6 +255,12 @@ public sealed class HttpServer {
                             }
                         }
                     }
+                } else {
+                    var requiredParams = qparams.Where(x => !x.IsOptional).Select(x => $"'{x.Name}'").ToList();
+                    if (requiredParams.Any()) {
+                        await HandleDefaultErrorPageAsync(rc, HttpStatusCode.BadRequest, $"Missing required query parameter(s): {string.Join(",", requiredParams)}");
+                        return;
+                    }
                 }
                 convertedQParamValues[0] = rc;
                 rc.ParsedParameters = parsedQParams.AsReadOnly();