MDEV-11917 enum/set command-line options aren't respecting max-* settings.

my_option strucures for command-line variables should be set properly.

sql/sys_vars.ic

@@ -341,6 +341,8 @@ public:
                       substitute)
   {
     option.var_type|= GET_ENUM;
+    option.min_value= 0;
+    option.max_value= ULONG_MAX;
     global_var(ulong)= def_val;
     if ((option.u_max_value= (uchar**)max_var_ptr()))
     {
@@ -1349,6 +1351,8 @@ public:
                       substitute)
   {
     option.var_type|= GET_SET;
+    option.min_value= 0;
+    option.max_value= ~0ULL;
     global_var(ulonglong)= def_val;
     if ((option.u_max_value= (uchar**)max_var_ptr()))
     {