UI: Fix possible use-after-free of obs_source_t

Also removes an implicit pair of successive obs_source_getref and
obs_source_release calls from OBSSource.

UI/api-interface.cpp

@@ -114,8 +114,8 @@ struct OBSStudioAPI : obs_frontend_callbacks {
 		struct obs_frontend_source_list *sources) override
 	{
 		for (int i = 0; i < main->ui->transitions->count(); i++) {
-			obs_source_t *tr = main->ui->transitions->itemData(i)
-						   .value<OBSSource>();
+			OBSSource tr = main->ui->transitions->itemData(i)
+					       .value<OBSSource>();
 
 			if (!tr)
 				continue;

UI/window-basic-main-transitions.cpp

@@ -564,7 +564,7 @@ void OBSBasic::RenameTransition()
 {
 	QAction *action = reinterpret_cast<QAction *>(sender());
 	QVariant variant = action->property("transition");
-	obs_source_t *transition = variant.value<OBSSource>();
+	OBSSource transition = variant.value<OBSSource>();
 
 	string name;
 	QString placeHolderText = QT_UTF8(obs_source_get_name(transition));

UI/window-basic-main.cpp

@@ -733,7 +733,7 @@ obs_data_array_t *OBSBasic::SaveProjectors()
 		switch (type) {
 		case ProjectorType::Scene:
 		case ProjectorType::Source: {
-			obs_source_t *source = projector->GetSource();
+			OBSSource source = projector->GetSource();
 			const char *name = obs_source_get_name(source);
 			obs_data_set_string(data, "name", name);
 			break;
@@ -5393,8 +5393,8 @@ void OBSBasic::on_actionAddScene_triggered()
 		auto undo_fn = [](const std::string &data) {
 			obs_source_t *t = obs_get_source_by_name(data.c_str());
 			if (t) {
-				obs_source_release(t);
 				obs_source_remove(t);
+				obs_source_release(t);
 			}
 		};
 

UI/window-basic-preview.cpp

@@ -2302,10 +2302,7 @@ static obs_source_t *CreateLabel(float pixelRatio)
 	const char *text_source_id = "text_ft2_source";
 #endif
 
-	OBSSource txtSource =
-		obs_source_create_private(text_source_id, NULL, settings);
-
-	return txtSource;
+	return obs_source_create_private(text_source_id, NULL, settings);
 }
 
 static void SetLabelText(int sourceIndex, int px)