[mythtv] Backend dies when frontend lists tuner status for a tuner not bound to an input

[Philippe]

When a tuner is not bound to an input and the  frontend status window 
queries tuner status, the backend dies (likely in HandleRemoteEncoder)

The following modification in mythfrontend/statusbox.cpp fixed the 
problem for me :
In StatusBox::doTunerStatus()
change
WHERE parentid='0'
to
WHERE parentid='0' AND cardid IN (SELECT cardid FROM cardinput)

since it lists only the tuners bound to an input but it might not be the 
only/best way


Philippe