patch 8.2.2412: not all fields in "cstack" are initialized

Problem:    Not all fields in "cstack" are initialized which might cause a
            crash.
Solution:   Use CLEAR_FIELD().
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 3dec65e..8b9db68 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -696,11 +696,8 @@
     ++call_depth;
 
 #ifdef FEAT_EVAL
+    CLEAR_FIELD(cstack);
     cstack.cs_idx = -1;
-    cstack.cs_looplevel = 0;
-    cstack.cs_trylevel = 0;
-    cstack.cs_emsg_silent_list = NULL;
-    cstack.cs_lflags = 0;
     ga_init2(&lines_ga, (int)sizeof(wcmd_T), 10);
 
     real_cookie = getline_cookie(fgetline, cookie);