bugfix: duplicate character on enter

Dependencies

• [2] NJ6ZL7PW split lines on enter
• [3] I7MA5UOO move
• [4] 6LJZN727 handle chords
• [*] BJ5X5O4A let's prevent the text cursor from ever getting on a drawing
• [*] OTIBCAUJ love2d scaffold

Change contents

• edit in manual_tests at line 10
  [6.326]
  +

  + enter

  + cursor_pos == 0 -> insert empty line above current line
• replacement in main.lua at line 273
  [2.211]→[2.211:295](∅→∅)
  − Lines[Cursor_line].data = string.sub(Lines[Cursor_line].data, 1, byte_offset)
  [2.211]

  [2.295]
  + Lines[Cursor_line].data = string.sub(Lines[Cursor_line].data, 1, byte_offset-1)