Emit LIMIT -1 when offset is used without limit (#821)

* Emit LIMIT -1 when offset is used without limit, closes #816

SQLite requires a LIMIT clause to appear before OFFSET, so passing offset
without limit generated invalid SQL such as:

    select * from "t" offset 2

which raised OperationalError: near "2": syntax error.

A negative limit means "no upper bound" in SQLite, so "limit -1 offset N"
returns all rows from position N onwards.

Fixed in three places that build LIMIT/OFFSET SQL:

- Queryable.rows_where() - also covers pks_and_rows_where()
- Table.search_sql() - also covers search()
- the "sqlite-utils rows" CLI command

* Remove duplicate comments

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Co-authored-by: ethanhawkes-gif <259455325+ethanhawkes-gif@users.noreply.github.com>

sqlite_utils/cli.py

@@ -2478,6 +2478,8 @@ def rows(
     if limit:
         sql += f" limit {limit}"
     if offset:
+        if not limit:
+            sql += " limit -1"
         sql += f" offset {offset}"
     ctx.invoke(
         query,