Before it checked if the value was empty, which is true when
the value is 0. If this was the case, set it as default to 2

This patch checks instead if it is set, and only then sets the
default of 2. This allows you to select the option 0 (None)

Also makes sure that the online users block is not shown when
there are no users to display (ie, all institutions that the user
is in have None selected)

Change-Id: Ib168d9796484dacbb8d58d111127c9bf21069a59
Signed-off-by: Hugh Davenport <hugh@catalyst.net.nz>