Duplicate lints for line_length_linter

[AshesITR]

Found during vignette writing for #660

lintr::lint("x <- 2 # -------------------------------------------------------------------------------\n", 
            parse_settings = FALSE)
#> <text>:1:1: style: Lines should not be more than 80 characters.
#> x <- 2 # -------------------------------------------------------------------------------
#> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#> <text>:1:1: style: Lines should not be more than 80 characters.
#> x <- 2 # -------------------------------------------------------------------------------
#> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

^{Created on 2020-12-06 by the reprex package (v0.3.0)}

Happens only if the offending line contains R code.
I assume the problem is we lint over full_parsed_content plus parsed_content.