getVirtualSelect method to rework

[romainruaud]

As we seen together, there is a problem with getVirtualSelect in Category Datasource.

The actual version is too wide and is catching event non-virtual categories, which produces doublons like this (where category 12 is not virtual) :

This seems to occur only when positions have been fixed to some products on a non-virtual category.

"category": [
            {
              "category_id": 2
            },
            {
              "category_id": 11,
              "name": "Men"
            },
            {
              "category_id": 12,
              "position": 1,
              "name": "Tops"
            },
            {
              "category_id": 14,
              "is_parent": true,
              "name": "Jackets"
            },
            {
              "category_id": 12,
              "is_virtual": "1",
              "position": 1,
              "name": "Tops"
            }
          ]

[afoucret]

Fixed in branch 2.5.x and master.
You can test it.