[pvr.tvh] Added support for state "missed" to ParseRecordingUpdate().

tvh sets the state to "missed" under some circumstances. => https://github.com/tvheadend/tvheadend/blob/master/src/htsp_server.c#L706, but support for this state was missing in pvr.tvh. 

This led to a situation where my XBMC was thinking it would do an "endless" recording, because it never received an update for the started recording. Reason: pvr.tvh did not call TriggerTimerUpdate() for the case were noting changed in the pvrreocrdingupdate event but the "state" (went  to "missed" => variable update was false => no call to TriggerTimerUpdate).

BTW: pvr.hts also does not support state "missed", but is not affected by this bug, as it always calls TriggerTimerUpdate, regardless of a real change in data. :-/