UI: Fix studio mode always duplicating scene

If scene duplication mode is disabled and studio mode is turned on, it
would always initially duplicate scene regardless of whether scene
duplication mode was activated or not.

obs/window-basic-main-transitions.cpp

@@ -755,10 +755,16 @@ void OBSBasic::SetPreviewProgramMode(bool enabled)
 
 		OBSScene curScene = GetCurrentScene();
 
-		obs_scene_t *dup = obs_scene_duplicate(curScene, nullptr,
-				editPropertiesMode ?
-				OBS_SCENE_DUP_PRIVATE_COPY :
-				OBS_SCENE_DUP_PRIVATE_REFS);
+		obs_scene_t *dup;
+		if (sceneDuplicationMode) {
+			dup = obs_scene_duplicate(curScene, nullptr,
+					editPropertiesMode ?
+					OBS_SCENE_DUP_PRIVATE_COPY :
+					OBS_SCENE_DUP_PRIVATE_REFS);
+		} else {
+			dup = curScene;
+			obs_scene_addref(dup);
+		}
 
 		obs_source_t *transition = obs_get_output_source(0);
 		obs_source_t *dup_source = obs_scene_get_source(dup);