Don't remove old workspace

[dipunm]

It seems gnome does this for us now so this function causes the whole desktop to crash. :(

see: #22

[Jangberry]

It seems like it crashes only when it tries deleting the workspace while there still is a window on it. Like I patched it correcting it by if (fullScreenWorkspace.list_windows().length == 0) {global.workspaceManager.remove_workspace(fullScreenWorkspace, global.get_current_time());}
Don't know wich one is the best just dropping my findings
Nevermind it provokes an other bug, more rare but more vicious