handle missing cursors in settings

Dependencies

• [2] SDO4DHNU source: load cursor position from settings
• [3] JMUD7T3O get rid of ugly side-effects in tests
• [4] KKMFQDR4 editing source code from within the app

Change contents

• replacement in source.lua at line 132
  [3.169643]→[2.181:394](∅→∅)
  − File_navigation.cursors = settings.cursors

  − Editor_state.screen_top1 = File_navigation.cursors[Editor_state.filename].screen_top1

  − Editor_state.cursor1 = File_navigation.cursors[Editor_state.filename].cursor1
  [3.169643]

  [3.169733]
  + if settings.cursors then

  + File_navigation.cursors = settings.cursors

  + Editor_state.screen_top1 = File_navigation.cursors[Editor_state.filename].screen_top1

  + Editor_state.cursor1 = File_navigation.cursors[Editor_state.filename].cursor1

  + else

  + -- migrate old settings

  + Editor_state.screen_top1 = {line=1, pos=1}

  + Editor_state.cursor1 = {line=1, pos=1}

  + end