MDEV-10352 Server crashes in Field::set_default on CREATE TABLE

fix Item_default_value not to pretend being const_item
if the field's default_value expression isn't parsed yet

mysql-test/r/default.result

@@ -3362,4 +3362,6 @@ a	b	t
 4	5	4 also expression DEFAULT(0)+0
 4	5	5 the value of the DEFAULT(a), that is b
 drop table t1;
+create table t1 (col1 int default(-(default(col1))));
+ERROR 01000: Expression for field `col1` is refering to uninitialized field `col1`
 # end of 10.2 test

mysql-test/t/default.test

@@ -2069,4 +2069,10 @@ insert into t1 values (b, 5, '5 the value of the DEFAULT(a), that is b');
 select * from t1 order by t;
 drop table t1;
 
+#
+# MDEV-10352 Server crashes in Field::set_default on CREATE TABLE
+#
+--error ER_EXPRESSION_REFERS_TO_UNINIT_FIELD
+create table t1 (col1 int default(-(default(col1))));
+
 --echo # end of 10.2 test

sql/item.cc

@@ -8853,9 +8853,11 @@ int Item_default_value::save_in_field(Field *field_arg, bool no_conversions)
 
 table_map Item_default_value::used_tables() const
 {
-  if (field && field->default_value && field->default_value->flags)
-    return field->default_value->expr->used_tables();
-  return static_cast<table_map>(0);
+  if (!field || !field->default_value)
+    return static_cast<table_map>(0);
+  if (!field->default_value->expr)                      // not fully parsed field
+    return static_cast<table_map>(RAND_TABLE_BIT);
+  return field->default_value->expr->used_tables();
 }
 
 /**