tvheadend: xbmc allows 'numeric' setting to be empty. fix

packages/addons/service/multimedia/tvheadend/source/bin/tvheadend.start

@@ -73,6 +73,9 @@ for driver_dvb in $(find /storage/.xbmc/addons/driver.dvb.*/bin/userspace-driver
 done
 
 # (wait for) at least 1 adapter (xbmc allows to set 0)
+# xbmc allows "numeric" type field to be empty. lets handle thaat
+[ "$NUM_ADAPTERS" = "" ] && NUM_ADAPTERS=1
+# 0 does not make sense. should be 1 or more
 [ $NUM_ADAPTERS -lt 1 ] && NUM_ADAPTERS=1
 if [ "$WAIT_FOR_FEINIT" == "true" ] ; then
   while [ true ] ; do