message: Fix issue with cat /dev/urandom
diff: @@ -893,7 +893,7 @@ impl Term {
  // Clear `lines` lines at bottom of area
  {
  let end = self.scroll_region.end;
  - let start = end - lines;
  + let start = Line(end.0.saturating_sub(lines.0));
  self.grid.clear_region(start..end, |c| c.reset(&template));
  }
  @@ -925,7 +925,7 @@ impl Term {
  // Clear `lines` lines starting from origin to origin + lines
  {
  - let end = origin + lines;
  + let end = min(origin + lines, self.grid.num_lines());
  self.grid.clear_region(origin..end, |c| c.reset(&template));
  }
  