don't crash on exit in cectray by preventing a new action from being started
display the "tv not responding" warning on top of other windows
don't crash LibCecSharp when receiving an alert with a NULL param (like the connection lost alert)
don't lock up on exit in cectray when receiving log messages while the window is disposing
suppress sending some commands when the tv is not present/responding to polls
still locking up when disposing, because the log callback is trying to write to the disposing ui. disconnect from a background thread instead when disposing