Fix texture flush from CPU WaitSync regression on OpenGL (#4289)

Ryujinx.Graphics.Gpu/Image/TextureGroup.cs

@@ -1431,10 +1431,21 @@ namespace Ryujinx.Graphics.Gpu.Image
                 return;
             }
 
-            handle.Sync(_context);
+            bool isGpuThread = _context.IsGpuThread();
+
+            if (isGpuThread)
+            {
+                // No need to wait if we're on the GPU thread, we can just clear the modified flag immediately.
+                handle.Modified = false;
+            }
 
             _context.Renderer.BackgroundContextAction(() =>
             {
+                if (!isGpuThread)
+                {
+                    handle.Sync(_context);
+                }
+
                 Storage.SignalModifiedDirty();
 
                 lock (handle.Overlaps)

Ryujinx.Graphics.Gpu/Image/TextureGroupHandle.cs

@@ -231,10 +231,6 @@ namespace Ryujinx.Graphics.Gpu.Image
         /// </summary>
         /// <param name="context">The GPU context used to wait for sync</param>
         public void Sync(GpuContext context)
-        {
-            bool needsSync = !context.IsGpuThread();
-
-            if (needsSync)
         {
             ulong registeredSync = _registeredSync;
             long diff = (long)(context.SyncNumber - registeredSync);
@@ -254,11 +250,6 @@ namespace Ryujinx.Graphics.Gpu.Image
 
             // If the difference is <= 0, no data is not ready yet. Flush any data we can without waiting or removing modified flag.
         }
-            else
-            {
-                Modified = false;
-            }
-        }
 
         /// <summary>
         /// Clears the action registered variable, indicating that the tracking action should be