`transform=True` fails when you have an index on a column name with an underscore

I'm using this project (sqlite_minutils) as a part of a FastHTML web app and came across a bug. I used `python=3.12` and `sqlite-minutils==3.37.0.post3`. Here's a minimal reproduction:

```python
#script.py

from fasthtml.common import Database
from datetime import datetime

db = Database('test.db')

class Request:
id: str
time: str
# run with time_check and its index commented out first
time_check: str

requests = db.create(Request, if_not_exists=True, transform=True)
requests.create_index(('time',), unique=True, if_not_exists=True)
# first run with this index creation commented out
requests.create_index(('time_check',), unique=True, if_not_exists=True)

for i in range(5):
requests.insert(Request(time=datetime.now()))
```
To reproduce, simply first comment out `time_check: str` and the index on `time_check`, run `python script.py`. Then uncomment `time_check` and its index creation and re-run `python script.py`. You will get the following error, which is caused by the query returning nothing, and the index `[0]` trying to grab what isn't there.

```bash
File venv/lib/python3.12/site-packages/sqlite_minutils/db.py:1910, in Table.transform_sql(self, types, rename, drop, pk, not_null, defaults, drop_foreign_keys, add_foreign_keys, foreign_keys, column_order, tmp_suffix, keep_table)
1908 for index in self.indexes:
1909 if index.origin not in ("pk"):
-> 1910 index_sql = self.db.execute(
1911 """SELECT sql FROM sqlite_master WHERE type = 'index' AND name = :index_name;""",
1912 {"index_name": index.name},
1913 ).fetchall()[0][0]
1914 assert index_sql is not None, (
1915 f"Index '{index}' on table '{self.name}' does not have a "
1916 "CREATE INDEX statement. You must manually drop this index prior to running this "
1917 "transformation and manually recreate the new index after running this transformation."
1918 )
1919 if keep_table:

IndexError: list index out of range
```

It looks like the parameter substitution fails when there is an extra underscore from the column name. If I do the same query manually using the `?` substitution syntax it works, and if I do the query manually typing out the index name verbatim it also works.

Bắt đầu trong sqlite_minutils/db.py tại Table.transform_sql, đặc biệt là phần tra cứu sqlite_master quanh dòng 1910, và chạy bản tái hiện issue bằng script.py. Kiểm tra truy vấn tên index có tham số với các tên chứa dấu gạch dưới; hoàn tất khi quá trình biến đổi kết thúc mà không có IndexError và giữ nguyên index bị ảnh hưởng.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.