Fixes fixSortColumn's Random Initial Sorting

When loading a GridField with several new items without a sort order (e.g. after uploading 10 images via GridFieldBulkEditingTools), it would previously apply a seemingly random order to them. This fix ensures that the order applied is the same order as the items were created (or uploaded) in.

**BEFORE:**
![](http://spdr.me/AsDb+)

**AFTER:**
![](http://spdr.me/i9fz+)