shell: Don't show navigation bar for unconnected machines
shell: Don't show navigation bar for unconnected machines

Otherwise we get a misleading "No results found" message.

martinpitt/cockpit,mvollmer/cockpit,garrett/cockpit,garrett/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,garrett/cockpit,garrett/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,garrett/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit