fixed issue when reordering plugins to second last position of other column that has more than 2 widgets

Reproduce steps:

Profile page of user
- add 3 widgets
- 2 widgets in column 1 and 1 widget in column 2
- move widget from column 2 between the 2 widgets in column 1
- refresh the page
- result is widget is positioned at the last position instead of between the 2 widgets

Reason is that the move algorithm always extracts 1 from the widget count, but that is only the case when moving to the same column.

This is also still the problem in Elgg 1.9