Addressed empty NCA lockup

- Updated LoadGuestApplication to use a CancellationTokenSource so we can properly asynchronously cancel and not hang (other things could listen to this too, or cancel it).
- Moved PrepareLoadScreen() to later in the pipeline (because cancelling LoadGuestApplication causes issues).
- Added Metadata read/write logging.
- Made AppHost inherit Disposable interface so that the garbage collector kicks in (side effect: made private Dispose() public)
- Added a WaitHandle to wait on either gpuDoneEvent or gpuCTS.Cancel event (LoadGuestApplication cancellation).
- Set invalid title ID for metadata.

src/Ryujinx.HLE/Loaders/Processes/ProcessLoader.cs

@@ -14,6 +14,7 @@ using Ryujinx.HLE.Loaders.Executables;
 using Ryujinx.HLE.Loaders.Processes.Extensions;
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
 using System.IO;
 using Path = System.IO.Path;
 
@@ -27,10 +28,15 @@ namespace Ryujinx.HLE.Loaders.Processes
 
         private ulong _latestPid;
 
-        public ProcessResult ActiveApplication
+        public ProcessResult? ActiveApplication
         {
             get
             {
+                return _processesByPid.GetValueOrDefault(_latestPid);
+                
+                // Using this if statement locks up the UI and prevents a new game from loading.
+                // Haven't quite deduced why yet.
+                
                 if (!_processesByPid.TryGetValue(_latestPid, out ProcessResult value))
                     throw new RyujinxException(
                         $"The HLE Process map did not have a process with ID {_latestPid}. Are you missing firmware?");
@@ -144,7 +150,7 @@ namespace Ryujinx.HLE.Loaders.Processes
         public bool LoadUnpackedNca(string exeFsDirPath, string romFsPath = null)
         {
             ProcessResult processResult = new LocalFileSystem(exeFsDirPath).Load(_device, romFsPath);
-
+            
             if (processResult.ProcessId != 0 && _processesByPid.TryAdd(processResult.ProcessId, processResult))
             {
                 if (processResult.Start(_device))

src/Ryujinx.HLE/Loaders/Processes/ProcessResult.cs

@@ -4,7 +4,6 @@ using LibHac.Ns;
 using Ryujinx.Common.Logging;
 using Ryujinx.Cpu;
 using Ryujinx.HLE.HOS.SystemState;
-using Ryujinx.HLE.Loaders.Processes.Extensions;
 using Ryujinx.Horizon.Common;
 
 namespace Ryujinx.HLE.Loaders.Processes
@@ -52,6 +51,7 @@ namespace Ryujinx.HLE.Loaders.Processes
 
             if (metaLoader is not null)
             {
+                Logger.Info?.Print(LogClass.Application,$"metaLoader: {metaLoader}");
                 ulong programId = metaLoader.ProgramId;
 
                 Name = ApplicationControlProperties.Title[(int)titleLanguage].NameString.ToString();
@@ -71,8 +71,15 @@ namespace Ryujinx.HLE.Loaders.Processes
                 ProgramId = programId;
                 ProgramIdText = $"{programId:x16}";
                 Is64Bit = metaLoader.IsProgram64Bit;
+            } 
+            
+            else
+            {
+                Logger.Error?.Print(LogClass.Application,$"metaLoader is null !!!");
+                ProcessId = 0;
+                return;
             }
-
+            
             DiskCacheEnabled = diskCacheEnabled;
             AllowCodeMemoryForJit = allowCodeMemoryForJit;
         }