src/vs/workbench/api/common/extHostNotebookDocument.ts/ExtHostNotebookDocument/_validateIndex
class ExtHostNotebookDocument:	private _validateIndex(index: number): number {
		index = index | 0;
		if (index < 0) {
			return 0;
		} else if (index >= this._cells.length) {
			return this._cells.length - 1;
		} else {
			return index;
		}
	}