Invalidate cache before cancelling tasks on LUT change

Reversing the order ensures that any render tasks that finish after the
cancel request will find the cache already invalidated, preventing stale
LUT-processed frames from being written back and shown in the viewer.

app/node/color/ociolut/ociolut.cpp

@@ -185,16 +185,17 @@ void OCIOLutNode::GenerateProcessor()
 	set_processor(processor);
 
 	// The processor has changed. In the main GUI process (QApplication), refresh
-	// the viewer by cancelling background cache jobs and invalidating the cache.
-	// The worker process uses QGuiApplication and has no RenderManager/Preview
-	// AutoCacher, so skip this step to avoid crashing.
+	// the viewer by invalidating the cache and cancelling background cache jobs.
+	// Invalidating first ensures any in-flight renders that complete afterwards
+	// won't write stale frames back. The worker process uses QGuiApplication and
+	// has no RenderManager/PreviewAutoCacher, so skip this step to avoid crashing.
 	if (qobject_cast<QApplication *>(QCoreApplication::instance())) {
+		InvalidateAll(kTextureInput);
 		if (RenderManager *rm = RenderManager::instance()) {
 			if (PreviewAutoCacher *cacher = rm->GetCacher()) {
 				cacher->CancelVideoTasks(false);
 			}
 		}
-		InvalidateAll(kTextureInput);
 	}
 }