restore_state (PDF::Writer)

          # File lib/pdf/writer.rb, line 1721
    1721:   def restore_state
    1722:     unless @state_stack.empty?
    1723:       state = @state_stack.pop
    1724:       @current_fill_color         = state.fill_color
    1725:       @current_stroke_color       = state.stroke_color
    1726:       @current_text_render_style  = state.text_render_style
    1727:       @current_stroke_style       = state.stroke_style
    1728:       stroke_style!
    1729:     end
    1730:     add_content("\nQ")
    1731:   end