Plugin proftpd_bytes: fix autoconf handling

plugins/ftp/proftpd_bytes

@@ -27,11 +27,10 @@ STATEFILE=$MUNIN_PLUGSTATE/xferlog-bytes.offset
 if [ "$1" = "autoconf" ]; then
         if [ -f "${LOGFILE}" -a -n "${LOGTAIL}" -a -x "${LOGTAIL}" ] ; then
 		echo yes
-		exit 0
 	else
-		echo no
-		exit 1
+		echo "no (missing logfile or 'logtail' executable)"
 	fi
+	exit 0
 fi
 
 if [ "$1" = "config" ]; then