[pvr.tvh] Fix doublefree in HTSPConnection::ReadMessage.

If htsmsg_binary_deserialize fails it frees buf by itself. See:
https://github.com/adamsutton/xbmc-pvr-addons/blob/master/lib/libhts/htsmsg_binary.c#L127
+
https://github.com/adamsutton/xbmc-pvr-addons/blob/master/lib/libhts/htsmsg_binary.c#L130
+
https://github.com/adamsutton/xbmc-pvr-addons/blob/master/lib/libhts/htsmsg.c#L181

I ran into this SIGABRT from time to time during Kodi startup. 

Reason for not working unmarshalling is subject for another investigation. I guess, it has something to do with tvh not yet available while pvr.tvh already calling it.