Ensure the logger factory is initialized.

src/Microsoft.Net.Http.Server/LogHelper.cs

@@ -34,7 +34,7 @@ namespace Microsoft.Net.Http.Server
         {
             if (factory == null)
             {
-                return null;
+                factory = new LoggerFactory();
             }
 
             return factory.Create(type.FullName);

src/Microsoft.Net.Http.Server/WebListener.cs

@@ -91,12 +91,19 @@ namespace Microsoft.Net.Http.Server
         private long? _requestQueueLength;
 
         public WebListener()
+            : this(new LoggerFactory())
+        {
+        }
+
+        public WebListener(ILoggerFactory factory)
         {
             if (!UnsafeNclNativeMethods.HttpApi.Supported)
             {
                 throw new PlatformNotSupportedException();
             }
 
+            _logger = LogHelper.CreateLogger(factory, typeof(WebListener));
+
             Debug.Assert(UnsafeNclNativeMethods.HttpApi.ApiVersion ==
                 UnsafeNclNativeMethods.HttpApi.HTTP_API_VERSION.Version20, "Invalid Http api version");
 
@@ -109,12 +116,6 @@ namespace Microsoft.Net.Http.Server
             _connectionCancellationTokens = new ConcurrentDictionary<ulong, ConnectionCancellation>();
         }
 
-        public WebListener(ILoggerFactory factory)
-            : this()
-        {
-            _logger = LogHelper.CreateLogger(factory, typeof(WebListener));
-        }
-
         internal enum State
         {
             Stopped,