Fix position sort with flat tables when no category filter is applied

[elidrissidev]

Description (*)

This PR will fix the issue when you sort the Product collection by position with flat tables ON, and you either didn't set the Category filter, or the Category doesn't exist (getId() returns null). The issue was what seems to be a redundant ORDER BY clause being added with cat_index_position (alias of catalog_category_product_index.position), which is only JOINed if the Category exists. There is already an ORDER BY clause being added below the removed code, with the condition of Category filter being present, so this shouldn't cause any change of behavior.

Fixed Issues (if relevant)

1. Fixes Sort by position does not work #2511

Manual testing scenarios (*)

// Make sure you're not on Admin store, as flat tables is only used for frontend
Mage::app()->setCurrentStore(1);

Mage::getResourceModel('catalog/product_collection')
  // Either give it a non-existent category or omit the filter
  ->addCategoryFilter(Mage::getModel('catalog/category')->load(1234))
  ->addAttributeToSort('position')
  ->load();

This snipped will throw the below error before this patch:

SQLSTATE[42S22]: Column not found: 1054 Unknown column 'cat_index_position' in 'order clause', query was: SELECT `e`.`entity_id`, `e`.`type_id`, `e`.`attribute_set_id` FROM `catalog_product_flat_1` AS `e` WHERE (e.status = 1) ORDER BY `cat_index_position` ASC, `e`.`entity_id` ASC"

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[luigifab]

For me it's working with a local env, but we don't use sort by position on our store.

[fballiano]

merged and v20ed