Plugin falls back to default after installation

If the job configuration hasn't been saved after installing
this plugin, the property is not found and null will be returned.
So assume that the user wants to enable this plugin by default
if he/she installs it.

jenkins.log had following exceptions.

    WARNING: Least load balancer failed will use fallback
    java.lang.NullPointerException
            at org.bstick12.jenkinsci.plugins.leastload.LeastLoadBalancer.isDisabled(LeastLoadBalancer.java:132)
            at org.bstick12.jenkinsci.plugins.leastload.LeastLoadBalancer.map(LeastLoadBalancer.java:83)
            at hudson.model.LoadBalancer$2.map(LoadBalancer.java:148)
            at hudson.model.Queue.maintain(Queue.java:1041)
            at hudson.model.Queue.pop(Queue.java:868)
            at hudson.model.Executor.grabJob(Executor.java:289)
            at hudson.model.Executor.run(Executor.java:210)


After installing this fix, they were gone.