Server crash caused by concurrent inserts into table with sequence default

Our company has experienced server crashes due to this reproducible bug. Follow the steps below to reproduce it.

```
create sequence foo;
create table bar (x int primary key default (next value for foo), y int);
```

On two different sessions, run the following. For me, this caused a DB server crash within about two minutes:

```
while 1=1 do
insert into bar ( y )
select <<<something>>> from <<<something>>>;
rollback;
end while;
```

This version of the insert does not appear to cause the server crash:
```
while 1=1 do
insert into bar (x,y)
select next value for foo, <<<something>>> from <<<something>>>;
rollback;
end while;
```

The core dump for this crash indicated this as the failure:
Item_func_nextval::val_int (this=0x7f1e78cca8a8) at /usr/src/debug/MariaDB-10.4.24/src_0/sql/item_func.cc:6877