avoid redundant writes on exit

Dependencies

• [2] VIU2FBNV make sure to save right when quitting
• [3] AVTNUQYR basic test-enabled framework
• [4] PX7DDEMO autosave slightly less aggressively
• [*] OTIBCAUJ love2d scaffold

Change contents

• replacement in main.lua at line 326
  [2.66]→[2.66:98](∅→∅)
  − save_to_disk(Lines, Filename)
  [2.66]

  [2.98]
  + if Next_save then

  + save_to_disk(Lines, Filename)

  + end