win_line: update w_last_cursorline always

Vim patch 8.1.0856 (54d9ea6) caused a performance regression in Neovim,
when `set conceallevel=1 nocursorline` was used, since then due to
refactoring in 23c71d5 `w_last_cursorline` would never get updated
anymore.

Adds/uses `redrawdebug+=nodelta` for testing this.

Fixes https://github.com/neovim/neovim/issues/11100.
Closes https://github.com/neovim/neovim/pull/11101.

src/nvim/option.c

@@ -4306,6 +4306,10 @@ static char *set_num_option(int opt_idx, char_u *varp, long value,
     if (value < 0) {
       errmsg = e_positive;
     }
+  } else if (pp == &p_wd) {
+    if (value < 0) {
+      errmsg = e_positive;
+    }
   }
 
   // Don't change the value and return early if validation failed.