Fixing issue with $return handling for HTTP binding in .NET

Author: fabiocav

sample/HttpTrigger-CSharp/function.json

@@ -8,7 +8,7 @@
         },
         {
             "type": "http",
-            "name": "res",
+            "name": "$return",
             "direction": "out"
         }
     ]

src/WebJobs.Script/Description/DotNet/DotNetFunctionDescriptorProvider.cs

@@ -196,7 +196,7 @@ internal static bool TryCreateReturnValueParameterDescriptor(Type functionReturn
             descriptor = null;
 
             var returnBinding = bindings.SingleOrDefault(p => p.Metadata.IsReturn);
-            if (returnBinding == null)
+            if (returnBinding == null || returnBinding is IResultProcessingBinding)
             {
                 return false;
             }

src/WebJobs.Script/Description/DotNet/DotNetFunctionInvoker.cs

@@ -232,7 +232,7 @@ protected override async Task InvokeCore(object[] parameters, FunctionInvocation
             // if a return value binding was specified, copy the return value
             // into the output binding slot (by convention the last parameter)
             var returnValueBinding = Metadata.Bindings.SingleOrDefault(p => p.IsReturn);
-            if (returnValueBinding != null)
+            if (returnValueBinding != null && !(returnValueBinding is IResultProcessingBinding))
             {
                 originalParameters[originalParameters.Length - 1] = result;
             }