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

---------

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

tests/test_cli.py

@@ -1183,6 +1183,11 @@ def test_query_memory_does_not_create_file(tmpdir):
             ["-c", "name", "--limit", "1", "--offset", "1"],
             '[{"name": "Pancakes"}]',
         ),
+        # --offset without --limit
+        (
+            ["-c", "name", "--offset", "1"],
+            '[{"name": "Pancakes"}]',
+        ),
         # --where
         (
             ["-c", "name", "--where", "id = 1"],