src/vs/workbench/contrib/scm/browser/dirtydiffDecorator.ts/ShowPreviousChangeAction/run
class ShowPreviousChangeAction:	run(accessor: ServicesAccessor): void {
		const outerEditor = this.outerEditor ?? getOuterEditorFromDiffEditor(accessor);

		if (!outerEditor) {
			return;
		}

		const controller = DirtyDiffController.get(outerEditor);

		if (!controller) {
			return;
		}

		if (!controller.canNavigate()) {
			return;
		}

		controller.previous();
	}