Fixed error handling in RequestExtensions minio#1041

Response error handling was unintentionally removed in a previous commit. Added it back to the `ExecuteTaskCoreAsync` method.
Fixed `NullReferenceException`-bug in the `HandleIfErrorResponse` method - `throw response.Exception;` does not make sense if the exception is null.

Minio/RequestExtensions.cs

@@ -1,4 +1,4 @@
-using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.CodeAnalysis;
 using System.Net;
 using Minio.Credentials;
 using Minio.DataModel;
@@ -126,8 +126,6 @@ await requestMessageBuilder.ResponseWriter(responseResult.ContentStream, cancell
                     request.Method == HttpMethod.Get)
                     responseResult.Exception = new MissingObjectLockConfigurationException();
             }
-
-            return responseResult;
         }
         catch (Exception ex) when (ex is not (OperationCanceledException or
                                        ObjectNotFoundException))
@@ -141,6 +139,9 @@ await requestMessageBuilder.ResponseWriter(responseResult.ContentStream, cancell
                 responseResult = new ResponseResult(request, ex);
             return responseResult;
         }
+
+        minioClient.HandleIfErrorResponse(responseResult, errorHandlers, startTime);
+        return responseResult;
     }
 
     private static Task<ResponseResult> ExecuteWithRetry(this IMinioClient minioClient,
@@ -369,7 +370,7 @@ private static void HandleIfErrorResponse(this IMinioClient minioClient, Respons
             minioClient.LogRequest(response.Request, response, (now - startTime).TotalMilliseconds);
         }
 
-        if (response.Exception is null)
+        if (response.Exception is not null)
             throw response.Exception;
 
         if (handlers.Any())