serviceprobe: add NULL ptr check on dvb mux to be safe
Fix #1444 - dvr: ensure that DVR entries are not removed when EPG is updated

previously an overlapping (replacement) event could result in the DVR
entry being completely removed. This will now ensure that the original
entry is left in place (with just info and times).

It will also try and re-match with an EPG entry as and when it can.
Fix #1643 - dvb: close dvr device on each re-tune
dvb: fix problems with dvb satconf processing and storage