BUG #17998: Postgres crashes when executing WorkTableScan.

The following bug has been logged on the website:

Bug reference:      17998
Logged by:          Jerry
Email address:      chenglin-liang@outlook.com
PostgreSQL version: Unsupported/Unknown
Operating system:   Ubuntu 18.04.6
Description:

I developed a fuzzing tool that skips the optimizer and directly uses the
correct physical plan to fuzz postgres, and found a crash caused by
executing WorkTableScan.
For detailed steps to reproduce, see the
link:https://github.com/chenglinLiang/pg-report.

-- Environment --
PG version: 10.23
Platform: Ubuntu 18.04.6
Kernel: Linux 5.15.0-75-generic