.delete_where() returns [] when it should return self

[simonw]

If the table doesn't exist it should still return self, not []:

sqlite-utils/sqlite_utils/db.py

Lines 1676 to 1683 in ee469e3

	def delete_where(self, where=None, where_args=None):
	if not self.exists():
	return []
	sql = "delete from [{}]".format(self.name)
	if where is not None:
	sql += " where " + where
	self.db.execute(sql, where_args or [])
	return self

Spotted with mypy while working on #312.

[simonw]

Or should we raise an error if you attempt to call .delete_where() on a table that doesn't exist?