BUG #17514: Application with embedded SQL crashes when executing EXEC SQL PREPARE

The following bug has been logged on the website:

Bug reference:      17514
Logged by:          Okano Naoki
Email address:      okano.naoki@jp.fujitsu.com
PostgreSQL version: 12.9
Operating system:   RHEL 7
Description:

Hi, 

Application with embedded SQL crashes with segmentation fault if I execute
EXEC SQL PREPARE
command before executing EXEC SQL CONNECT command (*1).
I know that it is the correct operation to execute EXEC SQL CONNECT command
first 
and then execute EXEC SQL PREPARE command.
But I expect this wrong operation to result in an error, not a crash.
Is it correct that this operation causes the application to crash? Or is it
a bug?

[Environment]
* OS version: RHEL 7
* PostgreSQL version: 12
  I checked that PostgreSQL 10 and 14 also occurred a same issue.

(*1) Here is an exapmle.
int
main(void)
{
  EXEC SQL BEGIN DECLARE SECTION;
    char *connection = "tcp:postgresql://localhost/postgres";
    char *user = "user_name";
  EXEC SQL END DECLARE SECTION;

  ECPGdebug(1, stderr);

  /* Skip a CONNECT command deliberately. */
  /* EXEC SQL CONNECT TO :connection USER :user; */

  EXEC SQL PREPARE stmt1 FROM "SELECT * FROM pg_database WHERE oid = ?";
  return (0);
}


The following is a backtrace of the coredump.
(gdb) bt
#0  0x00007f9b4d4da150 in parseInput () from
/opt/rh/rh-postgresql12/root/usr//lib64/libpq.so.rh-postgresql12-5
#1  0x00007f9b4d4dc60d in PQgetResult () from
/opt/rh/rh-postgresql12/root/usr//lib64/libpq.so.rh-postgresql12-5
#2  0x00007f9b4d4dc8cf in PQexecStart () from
/opt/rh/rh-postgresql12/root/usr//lib64/libpq.so.rh-postgresql12-5
#3  0x00007f9b4d4dcb6c in PQprepare () from
/opt/rh/rh-postgresql12/root/usr//lib64/libpq.so.rh-postgresql12-5
#4  0x00007f9b4dd01a61 in prepare_common () from
/opt/rh/rh-postgresql12/root/usr//lib64/libecpg.so.rh-postgresql12-6
#5  0x00007f9b4dd01fb5 in ECPGprepare () from
/opt/rh/rh-postgresql12/root/usr//lib64/libecpg.so.rh-postgresql12-6
#6  0x0000000000400a79 in main ()

Thanks in advance.

Regards,
Naoki Okano