Error catching on range select

Will only now begin to select a range of files if we have selected files
already.
If not, it will add this first file as a start point.
Will also only range select if we are range selecting in the same
folder, otherwise will add this file. This enables you to select ranges
of files in different folders.
Lastly, the root has a very slightly different node structure, as we
can't start at 0 and step in increments of 2, it needs to be 1, 3, 5
etc. So as a failsafe, if the node we're looking at is not a LI,
increase the i counter by 1.