BUG #18657: Using JSON_OBJECTAGG with volatile function leads to segfault

The following bug has been logged on the website:

Bug reference:      18657
Logged by:          Alexander Lakhin
Email address:      exclusion@gmail.com
PostgreSQL version: 17.0
Operating system:   Ubuntu 22.04
Description:

The following query:
SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': random() RETURNING text) FORMAT
JSON);

triggers a server crash with the following stack trace:
Core was generated by `postgres: law regression [local] SELECT
                        '.
Program terminated with signal SIGSEGV, Segmentation fault.

#0  0x000055b54914ee1b in ExecBuildAggTrans (...) at execExpr.c:3514
3514                    expr_setup_walker((Node *)
pertrans->aggref->aggdirectargs,
(gdb) bt
#0  0x000055b54914ee1b in ExecBuildAggTrans (...) at execExpr.c:3514
#1  0x000055b549180ee9 in ExecInitAgg (...) at nodeAgg.c:4017
#2  0x000055b54916eb13 in ExecInitNode (...) at execProcnode.c:341
#3  0x000055b549162d3f in InitPlan (...) at execMain.c:968
#4  0x000055b549162732 in standard_ExecutorStart (...) at execMain.c:263
#5  0x000055b54916245a in ExecutorStart (...) at execMain.c:139
#6  0x000055b549411063 in PortalStart (...) at pquery.c:517
#7  0x000055b54940d172 in exec_simple_query (
    query_string=0x55b54b3f4430 "SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b':
random() RETURNING text) FORMAT JSON);") at postgres.c:1239

(gdb) p pertrans->aggref
$1 = (Aggref *) 0x0

First bad commit for this anomaly is b6e1157e7.