Fix issue with concurrent logging (#63)

* Fix issue with concurrent logging

* Fix namespace + code format/cleanup

src/WireMock.Net/Owin/GlobalExceptionMiddleware.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Threading.Tasks;
+using Newtonsoft.Json;
+#if !NETSTANDARD
+using Microsoft.Owin;
+#else
+using Microsoft.AspNetCore.Http;
+#endif
+
+namespace WireMock.Owin
+{
+#if !NETSTANDARD
+    internal class GlobalExceptionMiddleware : OwinMiddleware
+#else
+    internal class GlobalExceptionMiddleware
+#endif
+    {
+#if !NETSTANDARD
+        public GlobalExceptionMiddleware(OwinMiddleware next) : base(next) { }
+#else
+        public GlobalExceptionMiddleware(RequestDelegate next)
+        {
+            Next = next;
+        }
+#endif
+
+#if NETSTANDARD
+    public RequestDelegate Next { get; private set; }
+#endif
+
+    private readonly OwinResponseMapper _responseMapper = new OwinResponseMapper();
+
+#if !NETSTANDARD
+        public override async Task Invoke(IOwinContext ctx)
+#else
+        public async Task Invoke(HttpContext ctx)
+#endif
+        {
+            try
+            {
+                await Next?.Invoke(ctx);
+            }
+            catch (Exception ex)
+            {
+                await _responseMapper.MapAsync(new ResponseMessage { StatusCode = 500, Body = JsonConvert.SerializeObject(ex) }, ctx.Response);
+            }
+        }
+    }
+}