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

sqlite_utils/db.py

@@ -2003,6 +2003,10 @@ class Queryable:
         if limit is not None:
             sql += f" limit {limit}"
         if offset is not None:
+            # SQLite requires a limit clause before offset - a negative limit
+            # means "no upper bound", so offset works without an explicit limit
+            if limit is None:
+                sql += " limit -1"
             sql += f" offset {offset}"
         cursor = self.db.execute(sql, where_args or [])
         columns = dedupe_keys(c[0] for c in cursor.description)
@@ -3594,6 +3598,10 @@ class Table(Queryable):
         if limit is not None:
             limit_offset += f" limit {limit}"
         if offset is not None:
+            # SQLite requires a limit clause before offset - a negative limit
+            # means "no upper bound", so offset works without an explicit limit
+            if limit is None:
+                limit_offset += " limit -1"
             limit_offset += f" offset {offset}"
         return sql.format(
             dbtable=quote_identifier(self.name),