[PVR] Timeslot of EPG program

- In FixOverlappingEvents(), start time of EPG program from PVR client could be updated to fill the gap until the previous program. It is a  problem for the PVR client when a new timer is created from EPG. Often the start time of timeslot is use to identify the program. So here i update previous end time instead current start time to fill the gap or close overlap. With these changes EPG program keep the same start time along the flow: from the client, throw PVR and finally to the client when creating the timer.

- In GetTagAround() when previous program had no gap with current program (always true ? FixOverlappingEvents ?) the previous was returned instead the current begins around. So here time should be strickly less.