[Foundation] Always call the completion handler in a few callbacks in…

… NSUrlSessionHandler. (#20326)

Fixes these warnings:

    [API] API MISUSE: NSURLSession delegate System_Net_Http_NSUrlSessionHandler_NSUrlSessionHandlerDelegate: <System_Net_Http_NSUrlSessionHandler_NSUrlSessionHandlerDelegate: 0x600000676c60> (0x600000676c60)
    [API] API MISUSE: dataTask:didReceiveResponse:completionHandler: completion handler not called

    [API] API MISUSE: NSURLSession delegate System_Net_Http_NSUrlSessionHandler_NSUrlSessionHandlerDelegate: <System_Net_Http_NSUrlSessionHandler_NSUrlSessionHandlerDelegate: 0x600000676c60> (0x600000676c60)
    [API] API MISUSE: dataTask:willCacheResponse:completionHandler: completion handler not called

    [API] API MISUSE: NSURLSession delegate System_Net_Http_NSUrlSessionHandler_NSUrlSessionHandlerDelegate: <System_Net_Http_NSUrlSessionHandler_NSUrlSessionHandlerDelegate: 0x6000002cffa0> (0x6000002cffa0)
    [API] API MISUSE: dataTask:willCacheResponse:completionHandler: completion handler not called

which is printed numerous times with the test case here:

#11799 (comment)

src/Foundation/NSUrlSessionHandler.cs

@@ -852,11 +852,23 @@ void UpdateManagedCookieContainer (Uri absoluteUri, NSHttpCookie [] cookies)
 
 			[Preserve (Conditional = true)]
 			public override void DidReceiveResponse (NSUrlSession session, NSUrlSessionDataTask dataTask, NSUrlResponse response, Action<NSUrlSessionResponseDisposition> completionHandler)
+			{
+				try {
+					DidReceiveResponseImpl (session, dataTask, response, completionHandler);
+				} catch {
+					completionHandler (NSUrlSessionResponseDisposition.Cancel);
+					throw;
+				}
+			}
+
+			void DidReceiveResponseImpl (NSUrlSession session, NSUrlSessionDataTask dataTask, NSUrlResponse response, Action<NSUrlSessionResponseDisposition> completionHandler)
 			{
 				var inflight = GetInflightData (dataTask);
 
-				if (inflight is null)
+				if (inflight is null) {
+					completionHandler (NSUrlSessionResponseDisposition.Cancel);
 					return;
+				}
 
 				try {
 					var urlResponse = (NSHttpUrlResponse) response;
@@ -984,11 +996,24 @@ void SetResponse (InflightData inflight)
 
 			[Preserve (Conditional = true)]
 			public override void WillCacheResponse (NSUrlSession session, NSUrlSessionDataTask dataTask, NSCachedUrlResponse proposedResponse, Action<NSCachedUrlResponse> completionHandler)
+			{
+				try {
+					WillCacheResponseImpl (session, dataTask, proposedResponse, completionHandler);
+				} catch {
+					completionHandler (null!);
+					throw;
+				}
+			}
+
+			void WillCacheResponseImpl (NSUrlSession session, NSUrlSessionDataTask dataTask, NSCachedUrlResponse proposedResponse, Action<NSCachedUrlResponse> completionHandler)
 			{
 				var inflight = GetInflightData (dataTask);
 
-				if (inflight is null)
+				if (inflight is null) {
+					completionHandler (null!);
 					return;
+				}
+
 				// apple caches post request with a body, which should not happen. https://github.com/xamarin/maccore/issues/2571 
 				var disableCache = sessionHandler.DisableCaching || (inflight.Request.Method == HttpMethod.Post && inflight.Request.Content is not null);
 				completionHandler (disableCache ? null! : proposedResponse);
@@ -1002,11 +1027,24 @@ public override void WillPerformHttpRedirection (NSUrlSession session, NSUrlSess
 
 			[Preserve (Conditional = true)]
 			public override void DidReceiveChallenge (NSUrlSession session, NSUrlSessionTask task, NSUrlAuthenticationChallenge challenge, Action<NSUrlSessionAuthChallengeDisposition, NSUrlCredential> completionHandler)
+			{
+				try {
+					DidReceiveChallengeImpl (session, task, challenge, completionHandler);
+				} catch {
+					completionHandler (NSUrlSessionAuthChallengeDisposition.CancelAuthenticationChallenge, null!);
+					throw;
+				}
+			}
+
+			void DidReceiveChallengeImpl (NSUrlSession session, NSUrlSessionTask task, NSUrlAuthenticationChallenge challenge, Action<NSUrlSessionAuthChallengeDisposition, NSUrlCredential> completionHandler)
 			{
 				var inflight = GetInflightData (task);
 
-				if (inflight is null)
+				if (inflight is null) {
+					// Request was probably cancelled
+					completionHandler (NSUrlSessionAuthChallengeDisposition.CancelAuthenticationChallenge, null!);
 					return;
+				}
 
 				// ToCToU for the callback
 				var trustCallbackForUrl = sessionHandler.TrustOverrideForUrl;