Set the default of MaxTop to null

Author: xuzhg

src/Microsoft.AspNet.OData.Shared/Formatter/EdmLibHelpers.cs

@@ -934,7 +934,8 @@ private static ModelBoundQuerySettings GetMergedPropertyQuerySettings(
                         propertyTypeQuerySettings.PageSize;
                 }
 
-                if (mergedQuerySettings.MaxTop == 0 && propertyTypeQuerySettings.MaxTop != 0)
+                if (!mergedQuerySettings.MaxTop.HasValue ||
+                    (mergedQuerySettings.MaxTop == 0 && propertyTypeQuerySettings.MaxTop != 0))
                 {
                     mergedQuerySettings.MaxTop =
                         propertyTypeQuerySettings.MaxTop;

src/Microsoft.AspNet.OData.Shared/Query/DefaultQuerySettings.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNet.OData.Query
     /// </summary>
     public class DefaultQuerySettings
     {
-        private int? _maxTop = 0;
+        private int? _maxTop;
 
         /// <summary>
         /// Gets or sets a value indicating whether navigation property can be expanded.

src/Microsoft.AspNet.OData.Shared/Query/ModelBoundQuerySettings.cs

@@ -18,10 +18,7 @@ public class ModelBoundQuerySettings
         private Dictionary<string, bool> _orderByConfigurations = new Dictionary<string, bool>();
         private Dictionary<string, bool> _filterConfigurations = new Dictionary<string, bool>();
 
-        internal static ModelBoundQuerySettings DefaultModelBoundQuerySettings = new ModelBoundQuerySettings
-        {
-            _maxTop = 0
-        };
+        internal static ModelBoundQuerySettings DefaultModelBoundQuerySettings = new ModelBoundQuerySettings();
 
         /// <summary>
         /// Instantiates a new instance of the <see cref="ModelBoundQuerySettings"/> class