[ticket/12158] The pagination start value should be 0 when there are no items.

PHPBB3-12158
[ticket/12158] Add test data for 0 items to validate_start() test.

PHPBB3-12158
Merge pull request #1994 from prototech/ticket/12158

[ticket/12158] The pagination start value should be 0 when there are no items.