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_fts.py

@@ -112,6 +112,17 @@ def test_search_limit_offset(fresh_db):
     )
 
 
+def test_search_offset_without_limit(fresh_db):
+    table = fresh_db["t"]
+    table.insert_all(search_records)
+    table.enable_fts(["text", "country"], fts_version="FTS4")
+    assert [row["rowid"] for row in table.search("are", order_by="rowid")] == [1, 2]
+    assert [
+        row["rowid"] for row in table.search("are", offset=1, order_by="rowid")
+    ] == [2]
+    assert table.search_sql(offset=1).strip().endswith("limit -1 offset 1")
+
+
 @pytest.mark.parametrize("fts_version", ("FTS4", "FTS5"))
 def test_search_where(fresh_db, fts_version):
     table = fresh_db["t"]