Handles trailing empty line at connectedInterfaces

EOS 4.14.1 sends and empty trailing line out the 'show interfaces status connected' in *text* mode. This was causing an error int the function connectedInterfaces when doing x.split()[ 0 ] : x was nil.
The added "if x" makes the check.
I have not tested other commands outputs, the trailing empty line (\n\n) might occur with other commands