Fix problem with 'set -e'

line 23 'set -e' cause the script to exit:

PID=$(pidof -x $DEAMON)
if [ -z $PID ]; then
    echo "$DEAMON is not running."
    exit $STATE_CRITICAL
fi

PID=$(pidof -x $DEAMON)  <- if $DEAMON doesn't exist, the script exit because of the 'set -e' (non-zero value returned).