Fix for CLI session hang on squeezebox duet

Check if the display type is none before sending the show command.  
Sending the show command to a player with display type none, such 
as a squeezebox duet, will hang the CLI session.  Since the show 
command is sent before switching to the waveinput favorite, the 
squeezebox will not start playing the stream.  

The show command is broken In squeezeserver 7.7.1 and possibly other 
versions.  The squeezebox server  bug is
http://bugs.slimdevices.com/show_bug.cgi?id=18026

I tested the change with a squeezebox duet and a classic.