message: Make the 'clear' command and ^L clearn and show a clear window.
  closes
diff: @@ -2593,7 +2593,7 @@ export class Emulator implements EmulatorApi {
  }
  private fillRight(x: number, y: number, ch: string = ' '): void {
  - const line = this._tryGetRow(y);
  + const line = this._getRow(y);
  if (line === null) {
  return;
  }
  