[mythtv] frontend hangs on livetv error

[James Armstrong]

Can the frontend be easily fixed so that it will either display a 
warning or just exit back to the menu when livetv fails? I get this 
every now and then when I am changing cards / inputs and there is no 
signal or low signal with the pcHDTV card. The frontend just sits at a 
black screen and I have to kill and restart:

Remote encoder not responding.
LiveTV not successfully started
Changing from None to WatchingLiveTV
Changing from None to None

It looks like the frontend knows about the problem but does not exit 
from livetv properly.

- James