vim-patch:8.2.2289: Vim9: 'cpo' can become empty (#19887)

Problem:    Vim9: 'cpo' can become empty.
Solution:   Use empty_option instead of an empty string.  Update quickfix
            buffer after restoring 'cpo'.  (closes vim/vim#7608)
e5a2dc87fd

Omit test as it is Vim9 script.

src/nvim/ex_eval.c

@@ -1376,7 +1376,7 @@ void ex_catch(exarg_T *eap)
           *end = NUL;
         }
         save_cpo = p_cpo;
-        p_cpo = "";
+        p_cpo = (char *)empty_option;
         // Disable error messages, it will make current exception
         // invalid
         emsg_off++;