Ensure ? is included in path variable. (#1271)

* Ensure ? is included in path variable closes #1270

* Added extra null check on request object

Author: jamestyne

src/React.Router/HtmlHelperExtensions.cs

@@ -102,7 +102,12 @@ public static IHtmlString ReactRouter<T>(
 			{
 				var response = htmlHelper.ViewContext.HttpContext.Response;
 				var request = htmlHelper.ViewContext.HttpContext.Request;
-				path = path ?? request.Path.ToString() + request.QueryString;
+				var queryString = request != null && request.QueryString != null ? request.QueryString.ToString() : "";
+				if (!string.IsNullOrWhiteSpace(queryString) && !queryString.StartsWith("?"))
+				{
+					queryString = $"?{queryString}";
+				}
+				path = path ?? request.Path.ToString() + queryString;
 
 				var reactComponent
 					= Environment.CreateRouterComponent(