message: Fix edge case of `:sort u`
  Fixes
diff: @@ -43,6 +43,8 @@ export class SortCommand extends node.CommandBase {
  originalLines.push(vimState.document.lineAt(currentLine).text);
  }
  + const lastLineLength = originalLines[originalLines.length - 1].length;
  +
  if (this.arguments.unique) {
  const seen = new Set<string>();
  const uniqueLines: string[] = [];
  @@ -56,8 +58,6 @@ export class SortCommand extends node.CommandBase {
  originalLines = uniqueLines;
  }
  - const lastLineLength = originalLines[originalLines.length - 1].length;
  -
  const sortedLines = this.arguments.ignoreCase
  ? originalLines.sort((a: string, b: string) => a.localeCompare(b))
  : originalLines.sort();
  