Fix remote screenshares not shown when local screenshare is being shown

The local screen was always shown, no matter if the user explicitly
switched to a remote screen. The local screen is part of the "screens"
array and has the same behaviour as the other screenshares, so the
visible one is the first element in the array.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>