apply viewport_x if vwidth gte bview width

previously the condition was vwidth gt bview width. this broke in the
very specific scenario when a line was exactly as wide as the bview
with soft-wrap disabled. if you invoked `cmd_move_eol` on this line,
we would detect that the cursor is off screen and skip
`tb_set_cursor`, however viewport_x also would not apply, so the
cursor would be invisible. making viewport_x apply in the gte case
fixes this.