sqlite3 Cursor NULL-deref via reentrant execute() inside a text_factory/converter during fetch

Bug report

Bug description:

import sqlite3
con = sqlite3.connect(":memory:")
con.execute("CREATE TABLE t(a TEXT, b TEXT)")
con.execute("INSERT INTO t VALUES ('first', 'second')")
cur = con.cursor()
def btf(data):
    try:
        cur.execute("SELECT 1")            
    except sqlite3.ProgrammingError:
        pass                              
    return bytes(data).decode()
con.text_factory = btf
cur.execute("SELECT a, b FROM t")
print(cur.fetchone())                  

Modules/_sqlite/cursor.c:402:23: runtime error: member access within null pointer of type 'struct pysqlite_Statement'
    #0 _pysqlite_fetch_one_row Modules/_sqlite/cursor.c:402
    #1 pysqlite_cursor_iternext Modules/_sqlite/cursor.c:1155
    #2 pysqlite_cursor_fetchone_impl Modules/_sqlite/cursor.c:1206
    #3 pysqlite_cursor_fetchone Modules/_sqlite/clinic/cursor.c.h:169

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-157578

Start with Modules/_sqlite/cursor.c, especially _pysqlite_fetch_one_row around line 402, and reproduce the report under a sanitizer using the text_factory callback shown. Trace how the reentrant cur.execute() affects the statement during fetch; done means the reproducer no longer reaches the null dereference and appropriate coverage is added alongside the existing linked work.