overflow-newline-into-fringe

overflow-newline-into-fringe is a variable defined in `C source code'.
Its value is

t

Documentation:
Non-nil means that newline may flow into the right fringe.
This means that display lines which are exactly as wide as the window
(not counting the final newline) will only occupy one screen line, by
showing (or hiding) the final newline in the right fringe; when point
is at the final newline, the cursor is shown in the right fringe.
If nil, also continue lines which are exactly as wide as the window.

You can customize this variable.