patch 9.0.0399: using :defer in expression funcref not tested

Problem:    Using :defer in expression funcref not tested.
Solution:   Add a test.  Fix uncovered problems.
diff --git a/src/proto/vim9execute.pro b/src/proto/vim9execute.pro
index d43b1e2..bb3d414 100644
--- a/src/proto/vim9execute.pro
+++ b/src/proto/vim9execute.pro
@@ -4,6 +4,8 @@
 void funcstack_check_refcount(funcstack_T *funcstack);
 int set_ref_in_funcstacks(int copyID);
 int in_def_function(void);
+ectx_T *clear_currrent_ectx(void);
+void restore_current_ectx(ectx_T *ectx);
 int add_defer_function(char_u *name, int argcount, typval_T *argvars);
 char_u *char_from_string(char_u *str, varnumber_T index);
 char_u *string_slice(char_u *str, varnumber_T first, varnumber_T last, int exclusive);