[PR #2056] Removed redundant optional unwrap in SessionDelegate.

Source/SessionDelegate.swift

@@ -462,8 +462,8 @@ extension SessionDelegate: URLSessionTaskDelegate {
         // Determine whether an error has occurred
         var error: Error? = error
 
-        if let taskDelegate = self[task]?.delegate, taskDelegate.error != nil {
-            error = taskDelegate.error
+        if request.delegate.error != nil {
+            error = request.delegate.error
         }
 
         /// If an error occurred and the retrier is set, asynchronously ask the retrier if the request