BUG #19631: currtid2() on a view with GROUP BY ctid crashes with XX000

The following bug has been logged on the website:

Bug reference: 19631
Logged by: Zheng Hacker
Email address: hackerzheng666(at)gmail(dot)com
PostgreSQL version: 19beta3
Operating system: Linux x86_64
Description:

PostgreSQL version: 20devel (commit bdbf662, 2026-08-19)
OS: Linux x86_64

Calling currtid2() on a view whose SELECT includes ctid in a GROUP BY
hits elog(ERROR) without errcode() in tid.c, producing SQLSTATE XX000.

Reproducer:

CREATE TABLE tid_tab (a int);
INSERT INTO tid_tab VALUES (1);
CREATE VIEW tid_view_with_ctid AS
SELECT ctid, a FROM tid_tab GROUP BY ctid, a;
SELECT currtid2('tid_view_with_ctid'::text, '(0,1)'::tid);
-- ERROR: XX000: currtid cannot handle this view
-- LOCATION: currtid_for_view, tid.c:435

Note: the view has a ctid column (so it passes the tididx check at
line 389 which does have a proper errcode), but the GROUP BY prevents
the code from resolving the TLE to a simple base-table Var, so it
falls through to the elog(ERROR) at line 435 which lacks errcode().

Expected: a proper SQLSTATE (e.g. 0A000 feature_not_supported).

Found by automated SQL fuzzing.
Credit: Zheng Wang, Yanjie Zhao, Yiyang Liu