vim-patch:8.2.4753: error from setting an option is silently ignored (#19888)

Problem:    Error from setting an option is silently ignored.
Solution:   Handle option value errors better.  Fix uses of N_().
31e5c60a68

src/nvim/runtime.c

@@ -923,7 +923,7 @@ static int add_pack_dir_to_rtp(char_u *fname, bool is_pack)
     xstrlcat(new_rtp, afterdir, new_rtp_capacity);
   }
 
-  set_option_value("rtp", 0L, new_rtp, 0);
+  set_option_value_give_err("rtp", 0L, new_rtp, 0);
   xfree(new_rtp);
   retval = OK;