Set error correctly

Author: johnno1962

Foundation/URLSession/URLSessionTask.swift

@@ -253,16 +253,17 @@ open class URLSessionTask : NSObject, NSCopying {
                     if let _protocol = self._protocol {
                         _protocol.startLoading()
                     }
-                    else {
+                    else if self.error == nil {
                         var userInfo: [String: Any] = [NSLocalizedDescriptionKey: "unsupported URL"]
                         if let url = self.originalRequest?.url {
                             userInfo[NSURLErrorFailingURLErrorKey] = url
                             userInfo[NSURLErrorFailingURLStringErrorKey] = url.absoluteString
                         }
-                        let error = NSError(domain: NSURLErrorDomain,
-                                            code: NSURLErrorUnsupportedURL,
-                                            userInfo: userInfo)
-                        _ProtocolClient().urlSessionTask(self, didFailWithError: URLError(_nsError: error))
+                        let urlError = URLError(_nsError: NSError(domain: NSURLErrorDomain,
+                                                                  code: NSURLErrorUnsupportedURL,
+                                                                  userInfo: userInfo))
+                        self.error = urlError
+                        _ProtocolClient().urlProtocol(task: self, didFailWithError: urlError)
                     }
                 }
             }
@@ -588,10 +589,10 @@ extension _ProtocolClient : URLProtocolClient {
 
     func urlProtocol(_ protocol: URLProtocol, didFailWithError error: Error) {
         guard let task = `protocol`.task else { fatalError() }
-        urlSessionTask(task, didFailWithError: error)
+        urlProtocol(task: task, didFailWithError: error)
     }
 
-    func urlSessionTask(_ task: URLSessionTask, didFailWithError error: Error) {
+    func urlProtocol(task: URLSessionTask, didFailWithError error: Error) {
         guard let session = task.session as? URLSession else { fatalError() }
         switch session.behaviour(for: task) {
         case .taskDelegate(let delegate):