after updating to targetSdkVersion=34, an implicit mutable intent could lead to a crash.

closes https://github.com/PhilippC/keepass2android/issues/2790

src/keepass2android-app/NullActivity.cs

@@ -0,0 +1,24 @@
+using Android.Content.PM;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace keepass2android
+{
+    [Activity(Label = AppNames.AppName,
+        MainLauncher = false,
+        Theme = "@style/Kp2aTheme_BlueNoActionBar",
+        Exported = true)] 
+    ///For autofill, we sometimes need to pass an intent to an inline presentation which never gets fired. We use this as a dummy activity.
+    public class NullActivity: Activity
+    {
+        protected override void OnCreate(Bundle savedInstanceState)
+        {
+            Kp2aLog.Log("NullActivity.OnCreate - this is unexpected.");
+            base.OnCreate(savedInstanceState);
+            Finish();
+        }
+    }
+}

src/keepass2android-app/services/AutofillBase/AutofillHelper.cs

@@ -30,9 +30,8 @@ namespace keepass2android.services.AutofillBase
             {
                 return null;
             }
-            //make sure we have a pendingIntent always not null
-            pendingIntent ??= PendingIntent.GetService(context, 0, new Intent(),
-                Util.AddMutabilityFlag(PendingIntentFlags.OneShot | PendingIntentFlags.UpdateCurrent, PendingIntentFlags.Mutable));
+            // If the pending intent is null, we need to create a dummy one to avoid a crash
+            pendingIntent ??= PendingIntent.GetActivity(context, 0, new Intent(context, typeof(NullActivity)), PendingIntentFlags.OneShot | PendingIntentFlags.UpdateCurrent | PendingIntentFlags.Immutable);
 
             var slice = CreateInlinePresentationSlice(
                 inlinePresentationSpec,

src/keepass2android-app/services/AutofillBase/AutofillServiceBase.cs

@@ -405,7 +405,7 @@ namespace keepass2android.services.AutofillBase
             var datasetBuilder = new Dataset.Builder(presentation);
             datasetBuilder.SetAuthentication(pendingIntent?.IntentSender);
 
-            AutofillHelper.AddInlinePresentation(this, inlinePresentationSpec, text, datasetBuilder, Resource.Drawable.baseline_close_24, null);
+            AutofillHelper.AddInlinePresentation(this, inlinePresentationSpec, text, datasetBuilder, Resource.Drawable.baseline_close_24, pendingIntent);
 
             foreach (var autofillId in autofillIds)
             {