vim-patch:8.2.3751: cannot assign a lambda to an option that takes a function

Problem:    Cannot assign a lambda to an option that takes a function.
Solution:   Automatically convert the lambda to a string. (Yegappan
            Lakshmanan, closes vim/vim#9286)

6409553b6e

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

src/nvim/spell.c

@@ -3145,7 +3145,7 @@ void ex_spelldump(exarg_T *eap)
   }
   char *spl;
   long dummy;
-  (void)get_option_value("spl", &dummy, &spl, OPT_LOCAL);
+  (void)get_option_value("spl", &dummy, &spl, NULL, OPT_LOCAL);
 
   // Create a new empty buffer in a new window.
   do_cmdline_cmd("new");