MHEG: Cache database lookups in GetChannelIndex

Signed-off-by: Lawrence Rust <lvr@softsystem.co.uk>
Signed-off-by: Stuart Morgan <smorgan@mythtv.org>
MHEG: allow escape key to exit liveTV in input register 5

Signed-off-by: Lawrence Rust <lvr@softsystem.co.uk>
Signed-off-by: Stuart Morgan <smorgan@mythtv.org>
Don't try to pop an entry from an empty list in SSDP::ProcessData. Inspired by patch from Lawrence Rust but changed to use IsEmpty() instead of size()